Samacheer Kalvi Class 12 Bio Botany Solutions Chapter 2 Classical Genetics

I. Choose the correct answer from the given option

 

Question 1. Extra nuclear inheritance is a consequence of presence of genes in
(b) Endoplasmic reticulum and mitochondria
(c) Ribosomes and chloroplast
(d) Lysosomes and ribosomes
Answer: (a) Mitochondria and chloroplasts
In simple words: Extranuclear inheritance happens because some genes are found in cell parts outside the nucleus, like mitochondria and chloroplasts. These special parts have their own genetic material.

🎯 Exam Tip: Remember that extranuclear inheritance is also called cytoplasmic inheritance, as these organelles are in the cytoplasm.

 

Question 2. In order to find out the different types of gametes produced by a pea plant having the genotype AaBb, it should be crossed to a plant with the genotype
(a) aaBB
(b) AaBB
(c) AABB
(d) aabb
Answer: (d) aabb
In simple words: To discover all the different kinds of gametes a plant with AaBb genes can make, you need to cross it with a plant that has all recessive genes (aabb). This is known as a test cross, helping to reveal the complete genetic makeup of the parent.

🎯 Exam Tip: A test cross with a homozygous recessive individual is crucial for determining an unknown genotype, as it allows all possible gametes from the unknown parent to be expressed in the offspring's phenotype.

 

Question 3. How many different kinds of gametes will be produced by a plant having the genotype AABbCC?
(a) Three
(b) Four
(c) Nine
(d) Two
Answer: (d) Two
In simple words: For a plant with AABbCC genes, only two types of gametes can be formed: ABC and AbC. This happens because the 'AA' and 'CC' gene pairs are homozygous, meaning they can only pass on one type of allele each, while 'Bb' is heterozygous and can pass on either B or b.

🎯 Exam Tip: To find the number of different gametes, use the formula \( 2^n \), where \( n \) is the number of heterozygous gene pairs. In this case, AABbCC has one heterozygous pair (Bb), so \( 2^1 = 2 \) gametes.

 

Question 4. Which one of the following is an example of polygenic inheritance?
(a) Flower colour in Mirabilis jalapa
(c) Pod shape in garden pea
(d) Skin colour in humans
Answer: (d) Skin colour in humans
In simple words: Polygenic inheritance means that many different genes all work together to control one trait. Human skin color is a good example because it's determined by several genes, leading to a wide range of skin tones.

🎯 Exam Tip: Look for traits that show a continuous range of variation (like height, weight, or skin color) rather than distinct categories; these are often examples of polygenic inheritance.

 

Question 5. In Mendel's experiments with garden pea round seed shape (RR) was dominant over wrinkled seeds (rr), Yellow cotyledon on (YY) was dominant over green cotyledon (yy). What are the expected phenotypes in the F2 generation of the cross RRYY x rryy?
(a) Only round seeds with green cotyledons
(b) Only wrinkled seeds with yellow cotyledons
(c) Only wrinkled seeds with green cotyledons
(d) Round seeds with yellow cotyledons and wrinkled seeds with yellow cotyledons
Answer: (d) Round seeds with yellow cotyledons and wrinkled seeds with yellow cotyledons
In simple words: When pure round yellow peas are crossed with pure wrinkled green peas, the F1 generation will all be round yellow. In the F2 generation, you will see a mix: most will be round yellow, but some will be wrinkled yellow, and there will also be round green and wrinkled green. This is due to the independent assortment of traits.

🎯 Exam Tip: For dihybrid crosses, remember the classic 9:3:3:1 phenotypic ratio in the F2 generation, which represents combinations of both dominant and recessive traits.

 

Question 6. Test cross involves
(a) Crossing between two genotypes with a recessive trait
(b) Crossing between two F₁ hybrids
(c) Crossing the F₁ hybrid with a double recessive genotype
(d) Crossing between two genotypes with dominant trait
Answer: (c) Crossing the F₁ hybrid with a double recessive genotype
In simple words: A test cross is done by mating an F1 hybrid (a plant that has one dominant and one recessive gene for a trait) with a plant that has two recessive genes for that same trait. This helps geneticists see which genes the F1 hybrid is carrying.

🎯 Exam Tip: The result of a test cross helps confirm if an organism showing a dominant trait is homozygous (purebred) or heterozygous (hybrid).

 

Question 7. In pea plants, yellow seeds are dominant to green. If a heterozygous yellow seed plant is crossed with a green seeded plant, what ratio of yellow and green seeded plants would you expect in F1 generation?
(a) 9:1
(b) 1:3
(c) 3:1
(d) 50:50
Answer: (d) 50:50
In simple words: If you cross a plant with one yellow and one green gene (heterozygous yellow) with a plant that has two green genes (green seeded), half of the offspring will have yellow seeds and half will have green seeds. This gives a 1:1 ratio, which is 50% yellow and 50% green.

🎯 Exam Tip: Drawing a Punnett square for this monohybrid cross (Yy x yy) quickly confirms the 1:1 phenotypic ratio for heterozygous x homozygous recessive crosses.

 

Question 8. The genotype of a plant showing the dominant phenotype can be determined by
(a) Back cross
(b) Test cross
(c) Dihybrid cross
(d) Pedigree analysis
Answer: (b) Test cross
In simple words: To find out the exact genetic makeup (genotype) of a plant that looks dominant (shows the dominant trait), you perform a test cross. This involves mating it with a plant that is completely recessive for that trait.

🎯 Exam Tip: A test cross is highly effective because a recessive parent can only contribute recessive alleles, making the offspring's phenotype directly reflect the alleles contributed by the dominant-looking parent.

 

Question 9. Select the correct statement from the ones given below with respect to dihybrid cross
(a) Tightly linked genes on the same chromosomes show very few combinations
(b) Tightly linked genes on the same chromosomes show higher combinations
(c) Genes far apart on the same chromosomes show very few recombinations
(d) Genes loosely linked on the same chromosomes show similar recombinations
Answer: (a) Tightly linked genes on the same chromosomes show very few combinations
In simple words: When genes are located very close to each other on the same chromosome, they tend to be inherited together. This means they don't mix and match much with other genes during reproduction, resulting in few new combinations of traits.

🎯 Exam Tip: The closer genes are on a chromosome, the less likely they are to be separated by crossing over, leading to high linkage and low recombination frequency.

 

Question 10. Which Mendelian idea is depicted by a cross in which the Fx generation resembles both the parents
(a) Incomplete dominance
(b) Law of dominance
(c) Inheritance of one gene
(d) Codominance
Answer: (d) Codominance
In simple words: Codominance is when both versions of a gene are fully expressed at the same time, without blending. This makes the offspring show traits from both parents side-by-side, like how a flower might have both red and white patches.

🎯 Exam Tip: Codominance is different from incomplete dominance, where traits blend to form a new, intermediate phenotype (e.g., red and white flowers making pink). In codominance, both original traits are distinctly visible.

 

Question 11. Fruit colour in squash is an example of
(a) Recessive epistasis
(b) Dominant epistasis
(c) Complementary genes
(d) Inhibitory genes
Answer: (b) Dominant epistasis
In simple words: Dominant epistasis is when one dominant gene completely covers up the effect of another gene at a different location. In squash, a dominant gene for white color stops any other color genes from showing, so the fruit is white.

🎯 Exam Tip: Dominant epistasis often results in modified dihybrid ratios, where one trait (like white color in squash) overpowers others, leading to a simplified phenotypic outcome.

 

Question 12. In his classic experiments on Pea plants, Mendel did not use
(a) Flowering position
(b) seed colour
(c) pod length
Answer: (c) Pod length
In simple words: Gregor Mendel studied seven traits in pea plants for his inheritance experiments. He looked at things like seed color, pod shape, and flower position, but pod length was not one of the traits he chose to investigate.

🎯 Exam Tip: Knowing Mendel's seven pea plant traits (seed shape/color, pod shape/color, flower color/position, stem height) is important for understanding basic genetics experiments.

 

Question 13. The epistatic effect, in which the dihybrid cross 9:3:3:1 between AaBb Aabb is modified as
(a) Dominance of one allele on another allele of both loci
(b) Interaction between two alleles of different loci
(c) Dominance of one allele to another allele of same loci
(d) Interaction between two alleles of some loci
Answer: (b) Interaction between two alleles of different loci
In simple words: Epistatic effects happen when genes at different locations interact, and one gene's effect covers up or changes the effect of another gene. This modifies the typical 9:3:3:1 ratio seen in dihybrid crosses.

🎯 Exam Tip: Epistasis is a form of gene interaction where the expression of one gene is affected by another non-allelic gene, often resulting in altered Mendelian ratios.

 

Question 14. In a test cross involving F1 dihybrid flies, more parental type offspring were produced than the recombination type offspring. This indicates
(a) The two genes are located on two different chromosomes
(b) Chromosomes failed to separate during meiosis
(c) The two genes are linked and present on the same chromosome
(d) Both of the characters are controlled by more than one gene
Answer: (c) The two genes are linked and present on the same chromosome
In simple words: If you get more offspring that look like the original parents than new combinations, it means the genes are close together on the same chromosome and tend to be inherited as a group. This is called gene linkage.

🎯 Exam Tip: A higher proportion of parental types in a test cross indicates that genes are linked, as they are less likely to undergo recombination (crossing over).

 

Question 15. The genes controlling the seven pea characters studied by Mendel are known to be located on how many different chromosomes?
(a) Seven
(c) Five
(d) Four
Answer: (a) Seven
In simple words: Even though Mendel studied seven traits, the genes for these traits are spread across different chromosomes in the pea plant. This allowed them to be inherited independently, which was key to Mendel's discoveries.

🎯 Exam Tip: Mendel's work benefited from the fact that the traits he chose were either on different chromosomes or far enough apart on the same chromosome to assort independently.

 

Question 16. Which of the following explains how progeny can possess the combinations of traits that none of the parents possessed?
(a) law of segregation
(b) Chromosome theory
(c) Law of independent assortment
(d) Polygenic inheritance
Answer: (c) Law of independent assortment
In simple words: Mendel's law of independent assortment states that genes for different traits are inherited separately from each other. This mixing and matching of genes can create offspring with new combinations of traits that were not present in either parent.

🎯 Exam Tip: Independent assortment is crucial for genetic variation, allowing for new combinations of alleles and phenotypes in offspring.

 

Question 17. “Gametes are never hybrid” This is a statement of
(a) Law of dominance
(b) Law of independent assortment
(c) law of segregation
(d) Law of random fertilization
Answer: (c) law of segregation
In simple words: The law of segregation says that when an organism makes reproductive cells (gametes), the two genes (alleles) for each trait separate from each other. So, each gamete only gets one allele, making it "pure" and never a mix (hybrid) for that trait.

🎯 Exam Tip: This law ensures that each gamete carries only one allele for each gene, which is fundamental to understanding how traits are passed down.

 

Question 18. Gene which suppresses other genes activity but does not lie on the same locus is called as
(a) Epistatic
(c) Hypostatic
(d) Codominant
Answer: (a) Epistatic
In simple words: An epistatic gene is like a boss gene that can turn off or hide the effects of another gene, even if they are located in different places on the chromosomes. This means its effect shows up instead of the other gene's effect.

🎯 Exam Tip: Remember that the gene whose expression is suppressed is called the hypostatic gene, while the gene doing the suppressing is the epistatic gene.

 

Question 19. Pure tall plants are crossed with the pure dwarf plants. In the F1 generation, all plants were tall. These tall plants of the F1 generation were selfed and the ratio of tall to dwarf plants obtained was 3 : 1. This is called
(a) Dominance
(b) Inheritance
(c) Codominance
(d) Heredity
Answer: (a) Dominance
In simple words: When a tall plant and a dwarf plant are bred, and all the first generation plants are tall, it means the tall trait is stronger and hides the dwarf trait. This is known as dominance, where one gene characteristic overpowers another.

🎯 Exam Tip: The 3:1 ratio in the F2 generation of a monohybrid cross is a classic indicator of simple Mendelian dominance, where the dominant trait reappears more frequently.

 

Question 20. The dominant epistatic ratio is
(a) 9:3:3:1
(b) 12:3:1
(c) 9:3:4
(d) 9:6:1
Answer: (b) 12:3:1
In simple words: When one dominant gene hides the effect of another gene, the usual 9:3:3:1 ratio from a dihybrid cross changes. For dominant epistasis, this new ratio becomes 12:3:1, because the dominant epistatic allele leads to a combined phenotype group.

🎯 Exam Tip: Recognize that modified Mendelian ratios (like 12:3:1 for dominant epistasis) are key indicators of gene interactions.

 

Question 21. Select the period for Mendel's hybridization experiments
(a) 1856-1863
(c) 1857-1869
Answer: (a) 1856-1863
In simple words: Gregor Mendel conducted his important experiments on pea plant hybridization between the years 1856 and 1863. This period was crucial for laying the groundwork of modern genetics.

🎯 Exam Tip: While Mendel's work was published in 1865, his actual experimental period was from 1856 to 1863.

 

Question 22. Among the following characters which one was not considered by Mendel in his experimentation pea ?
(a) Stem – Tall or dwarf
(b) Trichomal glandular or non – glandular
(c) Seed – Green or yellow
(d) Pod - Inflated or constricted
Answer: (b) Trichomal glandular or non – glandular
In simple words: Mendel focused on distinct, easily observable traits in pea plants like height, seed color, and pod shape. He did not study the presence or type of trichomes (hair-like growths) on the plants.

🎯 Exam Tip: Mendel selected traits with clear contrasting forms to simplify his analysis and ensure distinguishable results in his experiments.

 

Question 23. Name the seven contrasting traits of Mendel.
Answer: Mendel studied seven pairs of contrasting traits in pea plants. These traits are: Plant Height (tall/dwarf), Seed Shape (round/wrinkled), Cotyledon Color (yellow/green), Flower Color (purple/white), Pod Color (green/yellow), Pod Form (inflated/constricted), and Flower Position (axial/terminal). These distinct differences helped him understand inheritance patterns.
In simple words: Mendel looked at seven clear differences in peas: tall or short, round or wrinkled seeds, yellow or green seed insides, purple or white flowers, green or yellow pods, full or squeezed pods, and flowers on the side or at the end.

🎯 Exam Tip: Memorizing these seven traits helps in understanding Mendel's experimental design and the basis of his laws of inheritance.

 

Question 24. What is meant by true-breeding or pure breeding lines/strain?
Answer: True breeding lines, also called pure breeding strains, are organisms that consistently produce offspring with the same specific trait over many generations. This happens because they have undergone continuous self-pollination, making them homozygous for the traits being studied. Therefore, their parents are homozygous for every trait, ensuring consistent inheritance.

• True breeding means an organism will always pass down specific traits to its offspring when self-pollinated.
• These organisms are homozygous, meaning they have two identical alleles for each gene.
• This ensures that the specific phenotype trait is always inherited consistently from parent to offspring over many generations.

In simple words: True-breeding plants always produce offspring that look exactly like them for a certain trait. This is because they have matching genes for that trait and have been self-pollinating for a long time.

🎯 Exam Tip: True-breeding lines are essential for genetic experiments as they provide a reliable baseline for studying how traits are passed down.

 

Question 25. Give the names of the scientists who rediscovered Mendelism.
Answer: Mendel's experiments and findings were rediscovered by three biologists independently. These scientists were Hugo de Vries from Holland, Carl Correns from Germany, and Erich von Tschermak from Austria. Their separate work helped bring Mendel's forgotten principles of heredity to light. The rediscovery highlighted the universal nature of Mendel's laws.
In simple words: Three scientists named Hugo de Vries, Carl Correns, and Erich von Tschermak all found Mendel's work again many years after he first published it. They realized how important his ideas about how traits pass on truly were.

🎯 Exam Tip: Remember these three scientists as their independent discoveries solidified Mendel's place as the "Father of Genetics" long after his death.

 

Question 26. what is back cross?
Answer: A back cross is a genetic cross where an F1 offspring is crossed back with either one of its parental genotypes. This type of cross is often used to get desired traits back into a new variety or to identify the genotype of the F1 hybrid. It helps maintain the purity of the genetic line.

• A back cross is when an F1 generation offspring is crossed with one of its original parents.
• The recessive parent back cross helps scientists identify if the F1 hybrid is heterozygous.
• It involves crossing the F1 offspring with either of the parental lines to study specific gene inheritance.

In simple words: A back cross is when you breed a first-generation offspring back with one of its original parents. This helps to check its genes or to make a new generation more like the parent.

🎯 Exam Tip: While all test crosses are back crosses, not all back crosses are test crosses. A test cross specifically involves crossing with a homozygous recessive parent.

 

Question 27. Define Genetics.
Answer: Genetics is the branch of biological science that studies heredity and variation in living organisms. It specifically deals with the mechanisms by which traits are passed from parents to their offspring. The term "Genetics" was first introduced by William Bateson in 1906, establishing a dedicated field for this study. The study of genetics helps us understand why we look like our parents but also have unique traits.
In simple words: Genetics is the study of how traits are passed from parents to children and why living things are different from each other.

🎯 Exam Tip: When defining genetics, be sure to include both "heredity" (how traits are passed) and "variation" (differences among individuals).

 

Question 28. What are multiple alleles?
Answer: Multiple alleles refer to a situation where a gene has more than two alternative forms. While an individual organism only inherits two alleles for any given gene, many more alleles might exist within the larger population. This means that a gene for which at least two alleles exist is called polymorphic. For example, human ABO blood groups are controlled by three alleles (I^A, I^B, and i), not just two. These multiple forms contribute to greater genetic diversity.

• Alleles are different versions of a gene that cause variations in a trait.
• When a gene has three or more different allele forms in a population, it is called multiple alleles.
• For example, human blood types (ABO) are controlled by three alleles, not just two.

In simple words: Multiple alleles means there are more than two types of genes for one trait in a group of living things. Even though each person only has two of these genes, there are many types of genes in total for that one trait.

🎯 Exam Tip: Remember that multiple alleles describe the variation within a population, not necessarily within an individual, who will still only carry two alleles for a given gene.

 

Question 29. What are the reasons for Mendels successes in his breeding experiment? Pisum sativum a wise choice, because
Answer: Mendel's success in his breeding experiments with pea plants (Pisum sativum) was due to several strategic choices and methods. He carefully selected pea plants which have distinct contrasting traits, ensuring clear results. The pea plant itself was a wise choice because it is easy to grow, produces many offspring, and can be self-pollinated or cross-pollinated. Additionally, Mendel applied rigorous scientific methods, including statistical analysis, and kept meticulous records of his quantitative data. He ensured the purity of his parent lines by self-crossing them for many generations and studied one or two traits at a time to simplify his analysis. These careful steps helped him derive fundamental laws of inheritance.

• He used math and statistics in his biology experiments, along with probability laws.
• Mendel carefully followed scientific methods and kept accurate records with numbers from his crosses.
• His experiments were well-planned, and he used many samples of pea plants.
• The traits he studied had clear opposing forms (like tall or dwarf), controlled by genes on different chromosomes.
• Mendel made sure his parent plants were pure-breeding, testing their purity by self-crossing the offspring for many generations.

In simple words: Mendel was successful because he picked smart study plants (peas that had clear differences), used careful scientific steps, counted everything, and looked at one trait at a time. He also made sure his starting plants were pure.

🎯 Exam Tip: Highlight the quantitative approach, choice of organism, and careful experimental design as key factors in Mendel's groundbreaking discoveries.

 

Question 30. Explain the law of dominance in monohybrid cross.
Answer: The Law of Dominance, observed in a monohybrid cross, states that in a cross between parents with contrasting traits, only one form of the trait (the dominant trait) will appear in the F1 (first filial) generation. The other trait (recessive) remains hidden. However, this recessive trait reappears in the F2 generation, typically in a 3:1 ratio with the dominant trait. This demonstrates that genes for different traits are inherited separately. For example, when a pure tall pea plant (TT) is crossed with a pure dwarf pea plant (tt), all F1 plants are tall (Tt). When these F1 plants self-pollinate, the F2 generation shows a 3 tall:1 dwarf ratio, proving that the recessive allele was not lost but merely masked.

Regarding the F1 generation, the recessive allele is not truly lost; it simply remains hidden or masked by the dominant allele. It then reappears in the next generation.

In simple words: The law of dominance says that when you cross two different pure-breeding parents, only one trait (the dominant one) will show up in the first generation. The other trait (recessive) will be hidden but can reappear in the next generation.

🎯 Exam Tip: Always associate the Law of Dominance with the appearance of only one parental trait in the F1 generation and the reappearance of the hidden trait in F2 in a 3:1 ratio.

 

Question 31. Differentiate incomplete dominance and co-dominance.
Answer: Incomplete dominance and co-dominance are both types of gene interactions that differ from simple Mendelian dominance. In incomplete dominance, neither allele is completely dominant over the other, resulting in a blended or intermediate phenotype in heterozygotes. For example, if red and white flowers cross, the offspring might be pink. A new blended phenotype is formed. In co-dominance, however, both alleles are fully expressed simultaneously and equally in the heterozygote, without blending. This means both dominant traits are expressed conjointly. An example is the human ABO blood group system, where both A and B alleles can be expressed together (AB blood type). Another example is red and white flowers of camellia showing both colors as patches.
Incomplete Dominance:
1. In incomplete dominance, neither allele is completely dominant over another; instead, they combine to produce a new trait.
2. A new phenotype is formed due to the blending of characteristics (not alleles).
Co-dominance:
1. In co-dominance, both alleles in a heterozygote are dominant, and the traits are equally expressed (joint expression).
2. No new phenotype is formed; instead, both dominant traits are expressed together.
3. Example: Red and white flowers of camellia show both red and white patches.
In simple words: Incomplete dominance creates a mixed trait (like pink from red and white). Codominance shows both traits fully at the same time, without mixing, like stripes or spots of both colors.

🎯 Exam Tip: Remember the key difference: incomplete dominance results in a *blend*, while co-dominance results in *both traits showing distinctly*.

 

Question 32. What is meant by cytoplasmic inheritance?
Answer: Cytoplasmic inheritance, also known as extranuclear inheritance, refers to the transmission of genetic information found in the cytoplasm, outside the cell's nucleus. This typically involves genes located in organelles like chloroplasts and mitochondria, which have their own DNA. Unlike Mendelian inheritance, which follows nuclear chromosome patterns, cytoplasmic inheritance often shows uniparental (usually maternal) patterns because these organelles are primarily inherited from the female gamete. This type of inheritance helps explain traits that do not follow standard Mendelian ratios. It is a kind of non-Mendelian inheritance based on self-replicating extrachromosomal units.

• DNA is the universal genetic material found in all living organisms.
• Genes located in nuclear chromosomes follow Mendelian inheritance patterns.
• However, some traits are controlled by genes found in chloroplasts or mitochondria, which is known as extranuclear inheritance.
• This is a type of non-Mendelian inheritance because it does not follow Mendel's rules.
• Cytoplasmic organelles like chloroplasts and mitochondria act as inheritance vectors, leading to so-called cytoplasmic inheritance.
• This inheritance relies on self-replicating extrachromosomal units, like plasminogen, found within these cytoplasmic organelles.

In simple words: Cytoplasmic inheritance means that some traits are passed down through genes found in parts of the cell outside the main control center (nucleus), like in chloroplasts or mitochondria. It usually comes from the mother.

🎯 Exam Tip: Maternal inheritance is a strong indicator of cytoplasmic inheritance, as the mother typically contributes the cytoplasm and its organelles to the offspring.

 

Question 33. Describe dominant epistasis with an example.
Answer: Dominant epistasis occurs when a dominant allele at one gene locus (the epistatic gene) masks or suppresses the phenotypic expression of alleles at a different, non-allelic gene locus (the hypostatic gene). This interaction results in a modified phenotypic ratio, often 12:3:1 in a dihybrid cross, instead of the typical 9:3:3:1. The gene or locus whose expression is suppressed by an epistatic gene is known as the hypostatic gene. An example is fruit color in squash, where a dominant allele 'W' for white fruit color at one locus masks the expression of alleles for yellow 'G' or green 'g' color at another locus. Only if the 'W' allele is absent (i.e., 'ww'), do the colors 'G' and 'g' express themselves, leading to yellow or green fruit respectively. Thus, 'W' is epistatic to 'G' and 'g'.

Phenotypes: white fruit : yellow fruit : Green fruit
12 : 3 : 1
Phenotypic ratio: 12:3:1
In simple words: Dominant epistasis is when a dominant gene at one spot on a chromosome completely covers up the effect of another gene at a different spot. For example, in squash, a dominant gene for white color makes the fruit white, even if other genes are present for yellow or green.

🎯 Exam Tip: Remember that in dominant epistasis, the presence of just one dominant allele of the epistatic gene is enough to mask the expression of the hypostatic gene, leading to a modified 12:3:1 ratio.

 

Question 34. Explain polygenic inheritance with an example
Answer: Polygenic inheritance describes a type of inheritance where a single phenotypic trait is influenced by two or more different genes, rather than just one. This leads to continuous variation in the trait, meaning there's a wide range of possible phenotypes rather than distinct categories. Each gene contributes to the trait in an additive or cumulative way. Good examples include human skin color, eye color, and height, which are all determined by the combined effect of multiple genes. A classic study by H. Nilsson-Ehle (1909) on wheat kernel color illustrated polygenic inheritance, showing that kernel color is controlled by two genes, each with two alleles. When dark red (R1R1R2R2) and white (r1r1r2r2) varieties were crossed, the F1 generation had medium red kernels. In the F2 generation, a range of red intensities appeared, determined by the number of dominant 'R' genes present, from dark red (four R genes) to light red (one R gene) and white (no R genes).
In simple words: Polygenic inheritance is when many different genes work together to create one trait, like human skin color or height. Each gene adds a little bit to the final look, making a wide range of outcomes.

🎯 Exam Tip: Polygenic inheritance is characterized by continuous variation (a gradient of phenotypes) and additive effects of multiple genes, unlike Mendelian traits that show distinct categories.

 

Question 34. Explain polygenic inheritance with an example
Answer: Polygenic inheritance occurs when one characteristic or trait is controlled by two or more genes. This means that multiple genes contribute to a single trait, often resulting in a continuous range of phenotypes rather than distinct categories. Examples of polygenic inheritance include human skin color, eye color, and weight. In plants, the kernel color of wheat is a classic example of polygenic inheritance, as studied by H. Nilsson-Ehle in 1909. He found that wheat kernel color is controlled by two genes, each with two alleles. The red kernel color is dominant over white.
Consider a cross between pure breeding dark red wheat \( (R_1R_1R_2R_2) \) and pure breeding white wheat \( (r_1r_1r_2r_2) \).
In the \( F_1 \) generation, all offspring have the genotype \( (R_1r_1R_2r_2) \) and show a medium red color.
When these \( F_1 \) plants are self-crossed, the \( F_2 \) generation shows a range of kernel colors, from dark red to white. The intensity of the red color depends on the number of dominant 'R' genes present. For instance:
• Four \( R \) genes \( (R_1R_1R_2R_2) \) result in dark red.
• Three \( R \) genes \( (R_1R_1R_2r_2 \text{ or } R_1r_1R_2R_2) \) result in medium dark red.
• Two \( R \) genes \( (R_1R_1r_2r_2 \text{ or } R_1r_1R_2r_2 \text{ or } r_1r_1R_2R_2) \) result in medium red.
• One \( R \) gene \( (R_1r_1r_2r_2 \text{ or } r_1r_1R_2r_2) \) results in light red.
• Zero \( R \) genes \( (r_1r_1r_2r_2) \) result in white.
The \( F_2 \) generation exhibits five different phenotypic classes in a ratio of 1:4:6:4:1, representing the varying shades of red. The overall ratio of red to white kernels in the \( F_2 \) generation is 63:1. This continuous variation forms a bell-shaped curve when plotted, showing how multiple genes contribute to a single trait, where the more dominant alleles a plant has, the darker red its kernels will be.
In simple words: Polygenic inheritance means many genes work together to decide one trait. For example, in wheat plants, many 'R' genes control how red the kernel is. More 'R' genes mean a darker red, and no 'R' genes mean white. This creates a mix of colors rather than just one or two.

🎯 Exam Tip: When explaining polygenic inheritance, always mention the involvement of multiple genes for a single trait and provide a clear example like wheat kernel color or human skin color to illustrate the continuous variation.

 

Question 35. Differentiate continuous variation with discontinuous variation.
Answer: Variation refers to the differences among individuals within the same species. These differences can be caused by both inherited factors (genes) and environmental influences. Variation can be categorized into two main types: continuous and discontinuous. Continuous variation shows a wide range of phenotypes, often blending smoothly from one extreme to another, while discontinuous variation shows distinct, separate categories. For example, human height and weight are good examples of continuous variation, whereas human blood groups, gender identity, and eye color are examples of discontinuous variation.

In simple words: Continuous variation means traits like height that change smoothly, while discontinuous variation means traits like blood type that fall into clear groups. Continuous traits usually have many genes and are affected by the environment, creating a range of values.

🎯 Exam Tip: When distinguishing between continuous and discontinuous variation, remember that continuous variation involves traits that can be measured (like height), while discontinuous variation involves traits that fall into distinct categories (like blood type).

 

Question 36. Explain with an example how single genes affect multiple traits and alleles the phenotype of an organism.
Answer: While typically a single gene affects one trait, sometimes one gene can influence multiple, seemingly unrelated traits. This phenomenon is known as pleiotropy. In pleiotropy, a single gene codes for a protein or a regulatory molecule that affects several different biological pathways, leading to multiple phenotypic effects. For instance, the disease phenylketonuria (PKU) in humans is an example of pleiotropy, where a single gene mutation leads to intellectual disability, light skin and hair color, and a specific body odor. This is because the mutated gene fails to produce an enzyme needed to break down an amino acid, affecting brain development, pigment production, and metabolic pathways.
Another example is Marfan syndrome, a human genetic disorder caused by a mutation in a single gene that affects many aspects of growth and development, including unusual tall height, thin fingers and toes, dislocation of the eye lens, and heart problems in the aorta. In pea plants, the gene responsible for purple flower color also affects the seed color and a dark spot on the leaf axils. All these traits are inherited together because they are controlled by a single pleiotropic gene. Sickle cell anemia is also a pleiotropic disease, where a single gene mutation for abnormal hemoglobin leads to various health issues like anemia, organ damage, and increased resistance to malaria.
In simple words: Pleiotropy is when one gene affects many different traits. For example, in humans, one special gene might cause a person to be very tall, have thin fingers, and also have heart problems. All these different things come from a change in just one gene.

🎯 Exam Tip: When asked about pleiotropy, clearly define it as 'one gene, multiple effects' and provide distinct examples, like Marfan syndrome or PKU, explaining how a single gene affects various traits.

 

Question 37. Bring out the inheritance of chloroplast gene with an example.
Answer: Chloroplast inheritance, also known as extranuclear or maternal inheritance, refers to traits controlled by genes located in the chloroplast DNA, not the nuclear DNA. These traits are typically passed down only through the maternal parent, as the egg cell contributes most of the cytoplasm and its organelles (including chloroplasts) to the offspring, while the male gamete (pollen) usually contributes only its nucleus.
A classic example is the "4 O'clock plant" (Mirabilis jalapa). These plants can have dark green, pale green, or variegated (mixed green and white) leaves.
• If pollen from a dark green leaved plant (male) is transferred to the stigma of a pale green leaved plant (female), the \( F_1 \) generation will show dark green leaves.
• However, if the reciprocal cross is performed—pollen from a pale green leaved plant (male) to a dark green leaved plant (female)—the \( F_1 \) generation will consist of dark green plants, identical to the maternal parent.
This maternal effect clearly shows that the character is inherited through the cytoplasm provided by the female parent, not through the nuclear genes from both parents as Mendel's laws would predict. Therefore, the chloroplast genes, which reside in the cytoplasm, determine the leaf color. The pollen only provides the nucleus, and the chloroplasts come solely from the egg cell.Mirabilis jalapa pale green leaved plant (male) X dark green leaved plant (female) \( \downarrow \) \( F_1 \) Dark green leaved dark green leaved plant (male) X pale green leaved plant (female) \( \downarrow \) \( F_1 \) pale green leaved
In simple words: Chloroplast genes come from the mother plant only, through the egg cell's insides. The father plant's pollen only gives its core (nucleus), not the chloroplasts. So, the baby plant's leaf color is decided by the mother plant's chloroplasts, like in the 4 O'clock plant where the mother's leaf color is always passed on directly.

🎯 Exam Tip: Highlight that chloroplast inheritance is maternal and non-Mendelian. Emphasize the contribution of cytoplasm (from the egg) versus the nucleus (from pollen) to secure full marks.

I. Match the following

 

Question 1.
Answer:
(a) Tall - (iv) dwarf
(b) Purple - (i) white
(c) Arial - (iii) terminal
(d) Round - (ii) wrinkled
In simple words: This question matches traits with their contrasting forms, like tall with dwarf or purple with white.

🎯 Exam Tip: For 'match the following' questions, draw lines or list pairs to ensure each item is correctly linked, paying close attention to the specific contrasting traits.

 

Question 2.
Answer:
(a) Dominant epistasis - (ii) 12:3:1
(b) Duplicate genes - (iii) 15:1
(c) Recessive epistasis - (iv) 9:3:4
(d) Complementary gene - (i) 9:7
In simple words: This question matches different gene interactions with their typical genetic ratios, which show how traits are passed on.

🎯 Exam Tip: Memorize the characteristic phenotypic ratios associated with different types of gene interactions (epistasis, duplicate genes, complementary genes) as they are frequently tested.

 

Question 3.
Answer:
(a) Genetics - (ii) W. Batson
(b) Mendel - (iii) Father of Genetics
(c) Lethal gene - (i) E. Baeur
(d) H. Nilsson Ehle - (iv) Kernel colour
In simple words: This question links important scientists to their contributions or related concepts in genetics, like Mendel being the 'Father of Genetics'.

🎯 Exam Tip: Know the key figures in genetics and their main discoveries or associations, as these are common recall questions.

 

Question 4.
Answer:
(a) Polygenic inheritance - (iv) wheat kernel colour
(b) 4 O'clock pea plant - (iii) Mirabilis jalapa
(c) Garden pea plant - (i) Pisum sativum
(d) H. NillssanEhle - (ii) genetic material
In simple words: This question connects genetic concepts or scientists with their relevant examples, like Mendel's work with garden pea plants.

🎯 Exam Tip: Associate key genetic terms with their specific examples (e.g., polygenic inheritance with wheat kernel color) to demonstrate a deeper understanding.

II. Choose the correct statement

 

Question 5.
a) \( HbA \) and \( HbS \) alleles of normal and single-cell hemoglobin are multiple alleles
b) \( HbA \) and \( HbS \) alleles of normal and single-cell hemoglobin are dominant recessive allele
c) \( HbA \) and \( HbA \) alleles of normal and single cell heamoglobin are codominant allele
d) \( HbA \) and \( Hb \) & alleles of normal and single-cell hemoglobin are recessive alleles
Answer: (c) HbA and HbA alleles of normal and single cell heamoglobin are codominant allele
In simple words: When a person has both the \( HbA \) allele for normal hemoglobin and the \( HbS \) allele for sickle cell hemoglobin, both traits are shown at the same time. This is called codominance.

🎯 Exam Tip: Remember that in codominance, both alleles are expressed equally and distinctly in the heterozygote, as seen in the blood group system (AB blood type) and sickle cell trait.

 

Question 6.
a) When alleles of the contrasting characters are present together, one of the character expresses and the other remains hidden. There is the law of purity of gametes.
b) When alleles of the contrasting characters are present together, one of the character expresses and the other remains hidden. This is a law of dominance.
c) When alleles of the contrasting characters are present together with one of the character expresses and the other remain hidden This is law of segregation
d) When allele of two contrasting character are present together, one of the character express and remain hidden. This is law of independent assortment.
Answer: (b) When alleles of the contrasting characters are present together, one of the character expresses and the other remains hidden. This is a law of dominance
In simple words: The law of dominance states that if you have two different versions (alleles) of a gene, only one of them will show up or be "dominant" while the other stays hidden.

🎯 Exam Tip: Clearly differentiate between the Law of Dominance (one allele masks another) and the Law of Segregation (alleles separate during gamete formation) to avoid confusion.

 

Question 7.
a) Monohybrid ratio is 9:3:3:1
b) The crossing of \( F_1 \) to any one of the parent is called test cross
c) The phenotypic ratio of a monohybrid cross is 1:2:1
d) A cross in which parents differ in a single pair of contrasting character is called a dihybrid cross
Answer: (c) The phenotypic ratio of a monohybrid cross is 1:2:1
In simple words: The question asks about the common results in genetics. A monohybrid cross, which looks at one trait, usually shows a specific ratio of how those traits appear.

🎯 Exam Tip: Double-check whether the question is asking for the phenotypic ratio (what you see) or genotypic ratio (the genetic makeup) of a monohybrid cross, as the numbers are different.

 

Question 8.
a) The hybrid progeny in the first generation is called \( F_2 \)
b) The major reasons for the success of Mendelian experiment was the true-breeding of Garden Pea plant
c) X and Y are examples of alleles.
d) A pedigree chart shows the genotypes of any parent.
Answer: (b) The major reason for the success of mendelian experiment was true-breeding of Garden Pea plant
In simple words: Mendel was successful because he used pea plants that always produced the same traits, making it easy to see how features were passed down.

🎯 Exam Tip: Remember Mendel's choice of pea plants was crucial due to their easy cultivation, distinct traits, and ability to self-pollinate, ensuring true-breeding lines.

III. Choose the correct pair

 

Question 9.
a) Discontinuous variation - qualitative inheritance
b) Continuous variation - qualitative inheritance
c) Duplicate gene - 13: 3
d) Recessive epilate - 9:7
Answer: (a) Discontinuous variation - qualitative inheritance
In simple words: Discontinuous variation is when traits fall into clear groups (like blood type) and is about quality rather than a range of measurements.

🎯 Exam Tip: Qualitative inheritance describes traits that fit into distinct categories, directly correlating with discontinuous variation where phenotypes are clearly separate.

 

Question 10.
a) Monohybrid - 9:3:3:1
b) Dihybrid - 1: 2: 1
c) Recessive epistasis - 9: 3: 4
d) Extra chromosomal inheritance - Mendelian inheritance
Answer: (c) Recessive epistasis - 9: 3: 4
In simple words: Recessive epistasis is a type of gene interaction where a recessive allele at one gene hides the effect of another gene, which leads to a specific 9:3:4 ratio in the offspring.

🎯 Exam Tip: Learn the characteristic ratios for different gene interactions (like 9:3:4 for recessive epistasis) as they are key to understanding complex inheritance patterns.

 

Question 11.
a) Emasculation - removal of anther
b) Tt - homozygous
c) Genetic constitution - phenotype
d) Mono hybrid cross - law of independent assortment
Answer: (a) Emasculation - removal of anther
In simple words: Emasculation is a plant breeding technique where the male parts (anthers) of a flower are removed. This is done to prevent self-pollination and allow controlled crossing with pollen from another plant.

🎯 Exam Tip: Emasculation is a direct and simple concept; remember it specifically refers to the surgical removal of anthers to facilitate cross-pollination experiments.

IV. Choose the incorrect statement

 

Question 13.
a) A pedigree charts are shown which genes are co-dominant
b) A true-breeding is a kind of breeding where the parents would produce offspring that would carry the same phenotype
c) In polygenic inheritance, traits are determined by interaction of single gene
d) The interactions between separate genes, in which one masks the effect of another is called epistasis.
Answer: (c) In polygenic inheritance traits are determined by interaction of single gene
In simple words: The incorrect statement is that polygenic inheritance is determined by a single gene. Actually, polygenic inheritance means many genes work together to decide one trait.

🎯 Exam Tip: For 'incorrect statement' questions, read each option carefully and identify the one that contradicts fundamental genetic principles like polygenic inheritance involving multiple genes.

 

Question 14.
a) The outward appearance resulting from an individual's genotype for a particular characteristic is called phenotype
b) The recessive allele of the same gene represented by lower case letter.
c) Blood group is a human characteristic that shown discrete variation
d) The name given to different form of the same gene is gametes
Answer: (d) The name given to different form of the same gene is gametes
In simple words: The incorrect statement is that different forms of the same gene are called gametes. Different forms of the same gene are actually called alleles. Gametes are reproductive cells.

🎯 Exam Tip: Distinguish clearly between key genetic terms: phenotype (observable traits), genotype (genetic makeup), alleles (different forms of a gene), and gametes (sex cells). A common mistake is confusing alleles with gametes.

 

Question 15.
a) A pleiotropic gene is a single gene that more than one trait
b) A single gene affects multiple traits and alter the phenotype of the organism called as pleiotropy
c) An organism which has two different alleles of the gene is called homozygous
d) A person with one 'A' blood type and one 'B' blood type allele would have a blood type of "AB"
Answer: (c) An organism which has two different alleles of the gene is called homozygous
In simple words: The incorrect statement is that an organism with two different alleles is homozygous. Homozygous means having two identical alleles, while having two different alleles is called heterozygous.

🎯 Exam Tip: Ensure a solid understanding of homozygous (two identical alleles) vs. heterozygous (two different alleles), as these terms are fundamental in genetics questions.

 

Question 16.
a) A pleiotropic gene is a single gene that more than one trait
b) A single gene affects multiple traits and alter the phenotype of the organism called as pleiotropy
c) Marfans syndrome is an example of pleiotropy
d) One (or) single gene that cannot affect multiple traits are called pleiotropy.
Answer: (d) One (or) single gene that cannot affect multiple traits are called pleiotropy.
In simple words: The incorrect statement is that a single gene that cannot affect multiple traits is called pleiotropy. Pleiotropy means one gene *can* affect multiple traits.

🎯 Exam Tip: The core definition of pleiotropy is a single gene having multiple phenotypic effects. Any statement implying a lack of multiple effects for a single gene is incorrect in the context of pleiotropy.

V. Choose the Incorrect Pair

 

Question 17.
a) Genotype - Genetic makeup of organism
b) Recessive - A trait that is hidden
c) Probability - The chance that an event will take place
d) Independent assortment - Mendel's first law
Answer: (d) Independent assortment - Mendel's first law
In simple words: The incorrect pair is "Independent assortment - Mendel's first law." Independent assortment is Mendel's second law, not his first. Mendel's first law is the Law of Segregation.

🎯 Exam Tip: Clearly differentiate between Mendel's First Law (Law of Segregation) and Second Law (Law of Independent Assortment) to avoid common mistakes in matching questions.

 

Question 18.
a. Dominant Allele - RR
b. Recessive allele - rr
c. Heterozygous - Tt
d. Homozygous recessive - TT
Answer: (d) Homozygous recessive - TT
In simple words: The question asks to identify a characteristic with its correct genetic notation. Homozygous recessive refers to having two identical copies of a recessive allele (like 'tt' for dwarf), so 'TT' (homozygous dominant) is the contrasting example.

🎯 Exam Tip: Always double-check the definition of genetic terms (like dominant, recessive, homozygous, heterozygous) and their corresponding allele notations to avoid confusion in such matching questions.

 

Question 19.
a. Intra-locus interaction - allelic interactions
b. Inter-locus interaction - non-allelic interactions
c. Epistatic - allelic interactions
d. Polygenic interaction - non-allelic interaction
Answer: (c) Epistatic - allelic interactions
In simple words: Epistatic interaction happens when one gene affects how another gene is expressed. This type of interaction usually involves alleles, which are different versions of the same gene.

🎯 Exam Tip: Remember that epistatic interactions involve genes at different loci (locations) on chromosomes, but the *interaction itself* can be described in terms of alleles affecting each other's expression.

 

Question 20.
a. Complementary gene - 9:7
b. Co-dominance - 1:2:1
c. Dominant epistatics - 9:3:4
d. Inhibitor gene - 13:3
Answer: (c) Dominant epistatics - 9:3:4
In simple words: Dominant epistasis is a type of gene interaction where a dominant allele at one gene location hides the effect of another gene at a different location. This often changes the expected Mendelian ratios, like the 9:3:4 ratio seen here.

🎯 Exam Tip: Familiarize yourself with the modified Mendelian ratios that result from different types of gene interactions (epistasis, complementary genes, etc.) as they are common exam topics.

VI. Choose the Odd one out

 

Question 21.
Mobilis islan
b) Snapdragon
Answer: Due to incomplete options and missing answer in the source, this question cannot be processed.
In simple words: This question is incomplete.

🎯 Exam Tip: When faced with incomplete information in a question, it's best to identify what's missing and state that the question cannot be answered fully based on the provided data.

 

Question 22.
a. DNA
b. mitochondrial inheritance
c. Chloroplast inheritance
d. Atavism
Answer: (d) Atavism
In simple words: DNA, mitochondrial inheritance, and chloroplast inheritance are all related to genetic material and how it is passed on. Atavism is different because it is about the reappearance of an ancestral trait that was previously lost, which is not directly about genetic material itself in the same way.

🎯 Exam Tip: For "odd one out" questions, quickly define each option in your mind. The one that doesn't fit the common theme of the others is usually the answer.

 

Question 23.
a. Monohybrid cross
b. checkerboard
c. genotype
d. phenotype
Answer: (b) checkerboard
In simple words: A monohybrid cross, genotype, and phenotype are all core concepts in genetics. A checkerboard (or Punnett square) is a tool used to predict the outcomes of genetic crosses, making it the 'odd one out' in terms of being a method rather than a concept.

🎯 Exam Tip: Understand the difference between genetic concepts (like genotype, phenotype) and the tools used to study them (like Punnett squares or checkerboards).

 

Question 24.
a) co-dominance
b) Duplicate gene
c) inhibitor gene
d) supplementary gene
Answer: (b) Duplicate gene
In simple words: Duplicate gene interaction, inhibitor gene interaction, and supplementary gene interaction are all types of intergenic or non-allelic interactions, meaning they involve genes at different locations. Co-dominance is different because it is an intragenic interaction, involving alleles of the same gene.

🎯 Exam Tip: Classify gene interactions into intragenic (within the same gene) and intergenic (between different genes) categories. This helps distinguish them for "odd one out" questions.

VII. Assertion and Reason

 

Question 25. A: Polygenic inheritance R: Several genes combine to affect a single trait
(a) A is correct
(b) R is false
(c) R is the correct explanation of A
(d) R only correct
Answer: (c) R is the correct explanation of A
In simple words: Polygenic inheritance means that many different genes work together to control one trait. The reason (R) clearly states that several genes combine to affect a single trait, which perfectly explains what polygenic inheritance (A) is.

🎯 Exam Tip: For Assertion and Reason questions, first check if both statements are individually true. Then, see if the reason directly explains the assertion. Look for keywords like 'because' or 'therefore' to link them.

 

Question 26. A: Atavism is a modification of biological structure whereby an ancestral trait reappears after having been lost through evolutionary changes in the previous generation R: Reemergence of sexual reproduction in the flowering plant Hieracium pilosella is the best example for Atavism in plants
(a) A is correct R is the correct explanation of A
(b) A only true
(c) R only True
(d) A false & R is true
Answer: (a) A is correct R is the correct explana-tion of A
In simple words: Atavism is when a trait that was present in ancestors, but lost in recent generations, suddenly reappears. Both the assertion (A) and the reason (R) accurately describe atavism and provide a fitting example, with R explaining A.

🎯 Exam Tip: Ensure that the example given in the Reason is not only correct but also directly illustrates the concept described in the Assertion to be a correct explanation.

 

Question 27. A: The physical expression of an individual gene called phenotype R: Phenotype is physical observable charactertics of an organism
a) A & R True
c) A is correct
Answer: (c) A is correct
In simple words: Phenotype refers to the physical traits or characteristics that can be seen in an organism. So, the assertion (A) stating that the physical expression of a gene is called phenotype is a correct statement.

🎯 Exam Tip: Always have clear definitions for basic genetic terms like genotype and phenotype. Phenotype is what you observe, while genotype is the underlying genetic code.

 

Question 28. A: Interaction between two alleles of the same loci is the effect of epistasis R: The epistasis is the kind of intergenic and allelic interaction.
(a) A is correct R is false
(b) R alone correct
(c) R & A are true
(d) R is the correct explanation of A
Answer: (a) A is correct R is false
In simple words: Epistasis is about gene interaction where one gene hides or changes the effect of another gene at a *different* location (intergenic). Therefore, the assertion (A) that it's an interaction between two alleles of the *same* loci is incorrect, making R false as well in its description of *allelic* interaction.

🎯 Exam Tip: Carefully distinguish between 'allelic interaction' (involving different alleles of the *same* gene) and 'intergenic interaction' (involving genes at *different* loci) when defining epistasis.

VIII. Choose the best answer

 

Question 29. If you do dihybrid cross in Pisum sativum on the traits of pod shape and plant height, Will you get 9:3:3:1 ratio in F2 ?
a. Yes, because they are independently assorting genes.
b. No, they are linked genes.
c. Yes, because they are situated on different chromosomes
d. No, we can not do experiments on these two traits.
Answer: (a) Yes, because they are independently assorting genes.
In simple words: A dihybrid cross usually results in a 9:3:3:1 ratio in the F2 generation, but only if the genes for the two traits assort independently. This means they are on different chromosomes or far apart on the same chromosome.

🎯 Exam Tip: Remember that Mendel's 9:3:3:1 dihybrid ratio is only observed when genes assort independently, which means they are not linked.

 

Question 30.
Answer: Due to incomplete question text and options in the source, this question cannot be processed.
In simple words: This question is incomplete.

🎯 Exam Tip: If a question is severely truncated or lacks crucial information like a clear question stem or answer choices, it's impossible to provide a definitive answer.

 

Question 31. An allele is
a. a homozygous genotype
b. a heterozygous genotype
c. another word for gene
d. several possible form of gene
Answer: (c) another word for gene
In simple words: An allele is a different version or form of a gene. Genes control traits, and alleles are the specific instructions for those traits.

🎯 Exam Tip: Understand that while 'gene' is a general term for a unit of heredity, 'allele' refers to the specific variants of that gene (e.g., the gene for eye color has alleles for blue, brown, green eyes).

 

Question 32. Continuous variation is due to
a. effect of polygenes
b. effect of environment
c. effect of polygenes and environment
d. effect of one or two genes.
Answer: (c) effect of polygenes and environment
In simple words: Continuous variation, like height or weight, happens because many genes (polygenes) work together, and also because the environment (like diet or lifestyle) can influence the trait. Both factors play a role.

🎯 Exam Tip: Recognize that many complex traits (e.g., human height, skin color, intelligence) show continuous variation because they are influenced by both multiple genes (polygenic) and environmental factors.

 

Question 33. A variation in a characteristic in which individuals show two or a few traits with large differences between them.
Answer: Due to incomplete options and missing answer in the source, this question cannot be processed.
In simple words: This question is incomplete.

🎯 Exam Tip: Be aware that some questions might be about 'discontinuous variation' (where traits fall into distinct categories), which contrasts with 'continuous variation'.

 

Question 34. A trait that masks the expression of another trait when both versions of the gene are present in an individual
a. variation
b. recessive
c. co-dominance
d. dominant
Answer: (d) dominant
In simple words: A dominant trait is one that is always expressed, even if only one copy of its gene is present. It hides the effect of the recessive trait.

🎯 Exam Tip: Understand the core concept of dominance: a dominant allele expresses its trait even when paired with a recessive allele, while a recessive allele only expresses its trait when two copies are present.

 

Question 35. Which one of the following is not a correct pair regarding genes of pea plant,
a. Seed shape - Chromosome number 6
b. Pod colour - Chromosome number 5
c. Flower position - Chromosome number 4
d. Seed colour - Chromosome number 1
Answer: (a) Seed shape - Chromosome number 6
In simple words: Mendel's pea plant experiments involved seven traits, each located on a specific chromosome. Among the choices, the pairing of 'Seed shape' with 'Chromosome number 6' is identified as incorrect, as seed shape is actually on chromosome 7.

🎯 Exam Tip: While memorizing all chromosome locations isn't always necessary, understanding that different traits are typically found on different chromosomes is key to classical genetics.

 

Question 36.
Answer: Due to incomplete options and missing answer in the source, this question cannot be processed.
In simple words: This question is incomplete.

🎯 Exam Tip: For questions about the history of genetics, knowing who performed which experiments (e.g., Mendel) and the general scope of their work is often tested.

 

Question 37. Transmission of characters from parents to offsprings
a. variation
b. dominance
c. heredity
d. growth
Answer: (c) heredity
In simple words: Heredity is the passing of traits and characteristics from parents to their children through genes. It is why offspring often look similar to their parents.

🎯 Exam Tip: Heredity is the fundamental concept in genetics. Make sure you can clearly define it and differentiate it from related terms like variation or dominance.

 

Question 38. Species that shows a difference in the characteristics of the same natural population is called
a. heredity
b. variation
c.
d. -dominace
Answer: (b) variation
In simple words: Variation refers to the differences found among individuals of the same species. These differences can be in physical traits, behaviors, or even genetic makeup.

🎯 Exam Tip: Remember that variation is crucial for evolution, as it provides the raw material for natural selection to act upon.

 

Question 39.
Answer: Due to incomplete options and missing answer in the source, this question cannot be processed.
In simple words: This question is incomplete.

🎯 Exam Tip: Qualitative inheritance involves traits that fall into distinct categories (like red or white flowers), while quantitative (polygenic) inheritance involves traits that show a range of continuous values.

 

Question 40. "Experiments on plant hybrids" is a
a. book
b. research paper
c. journal
d. Magazine
Answer: (b) research paper
In simple words: Gregor Mendel's groundbreaking work on pea plants was published as a research paper titled "Experiments on Plant Hybrids." This paper laid the foundation for modern genetics.

🎯 Exam Tip: Knowing the titles of seminal works in science, like Mendel's paper, helps demonstrate a broader understanding of the subject's history.

 

Question 41. Mendels theory of inheritance is based on
a. Particulate theory
b. mass
c. hybridization
d. variation theor
Answer: (a) Particulate theory
In simple words: Mendel's theory says that traits are passed down through distinct "particles" (which we now call genes) from parents to offspring, rather than by blending. This concept helped explain how traits could reappear across generations.

🎯 Exam Tip: The particulate theory was revolutionary because it proposed that traits are inherited as discrete units, not as a blend, explaining why traits can skip generations and reappear.

 

Question 42. Removal of the anther is called
a. Atavism
b. Epistasis
c. Hybridization
d. Emasculation
Answer: (d) Emasculation
In simple words: Emasculation is a plant breeding technique where the anthers (the part of a flower that produces pollen) are removed. This is done to prevent self-pollination and ensure cross-pollination.

🎯 Exam Tip: Emasculation is a key step in controlled plant breeding experiments, ensuring that fertilization occurs only with desired pollen from another plant.

 

Question 43. Botanical name of garden pea is
a. Solanum tuberosum
b. Coccus nucitera
c. Pisum sativum
d. pea
Answer: (c) Pisum sativum
In simple words: The scientific name for the common garden pea, which Gregor Mendel used in his famous genetics experiments, is Pisum sativum. Using a scientific name helps biologists worldwide understand exactly which plant is being discussed.

🎯 Exam Tip: Knowing the scientific names of organisms commonly used in genetic studies (like *Pisum sativum* for pea plants) is important for biological literacy.

 

Question 44. Mendel's experiments were rediscovered by
a. Hugo de Vries & Carl Correns
b. E. Baur
c. H. Nilsson
d. T.H.Morgan
Answer: (a) Hugo de Vries & Carl Correns
In simple words: After Mendel's initial work went unnoticed for many years, three scientists independently rediscovered his findings. Hugo de Vries and Carl Correns are two of the most well-known of these scientists.

🎯 Exam Tip: It's important to remember that Mendel's work was initially overlooked but gained recognition decades later through the independent discoveries of several other scientists.

 

Question 45. If a homozygous red flowered plant is crossed with a homozygous white flower plant then the off-spring will be_
a. All red flowered
b. Half white flowered
c. Half red flowered
d. All white flowered
Answer: (c) Half red flowered
In simple words: When a pure red flower (RR) crosses with a pure white flower (WW), if the traits show incomplete dominance, the offspring will be pink (RW), meaning 'half red' in appearance. If it showed complete dominance, it would be all red.

🎯 Exam Tip: Pay close attention to whether the problem implies complete dominance (where one trait fully masks another) or incomplete dominance (where a blend or intermediate phenotype occurs) when predicting offspring traits.

 

Question 46. What is the best example for chloroplast inheritance
a. Mirabilis jalapa
b. Sorgum vulgare
c. Triticum vulgare
d. Musa paradisiaca
Answer: (a) Mirabilis jalapa
In simple words: Mirabilis jalapa, also known as the four o'clock plant, is famous for showing cytoplasmic or extranuclear inheritance, where traits (like leaf color) are passed down through the chloroplasts in the egg cell, not just through the nucleus.

🎯 Exam Tip: Mirabilis jalapa is a classic example used to illustrate maternal inheritance (cytoplasmic inheritance), where traits are passed down only from the mother due to organelles like chloroplasts.

 

Question 47. Among the pea plant cell which one has the ability to convert a precursor molecule into an active inform
a. Le:le
b. GA1
c. Le
d. le
Answer: (b) GA1
In simple words: In pea plants, the GA1 gene produces an enzyme that helps convert a precursor molecule into active gibberellin, which is a plant hormone that promotes stem growth. This is how the plant grows tall.

🎯 Exam Tip: Remember that genes often code for enzymes or proteins that are crucial for specific biochemical pathways, like hormone synthesis, affecting observable traits.

 

Question 48. Gene interaction concept was introduced and explained by
a. W. Bateson
b. Morgan
c. E. Baur
d. Nilsson
Answer: (a) W. Bateson
In simple words: William Bateson was a key figure in early genetics who introduced the concept of gene interaction, where multiple genes work together or influence each other to create a particular trait. He also coined the term 'genetics'.

🎯 Exam Tip: Associate W. Bateson with fundamental contributions to genetics, including introducing the term 'genetics' and the concept of gene interaction, which broadened the understanding beyond simple Mendelian inheritance.

 

Question 49. An allele which has the potential to cause the death of an organism is called
a. Genetic interaction
b. lethal alleles/lethal gene
c. Atavism
d. Autism
Answer: (b) lethal alleles/lethal genes
In simple words: Lethal alleles are specific versions of genes that, when inherited, can cause an organism to die, often before birth or early in development. They can be dominant or recessive.

🎯 Exam Tip: Lethal alleles often lead to modified Mendelian ratios (e.g., 2:1 instead of 3:1) in offspring because individuals with the lethal genotype do not survive.

 

Question 50. The gene whose expression is interfered by non- alletic gene and prevents from exhibiting its character is known as
a. hypostatic
b. epistatic
c. metastatic
d. hipostatic
Answer: (a) hypostatic
In simple words: In epistasis, one gene masks the effect of another. The gene whose expression is hidden or suppressed is called the hypostatic gene, while the gene that does the masking is called the epistatic gene.

🎯 Exam Tip: Differentiate between 'epistatic' (the gene that masks) and 'hypostatic' (the gene that is masked) when describing gene interactions.

 

Question 51. Height and skin colour in human are controlled by
a. two pair of genes
b. three pair of genes
c. five pair of genes
d. a pair of genes
Answer: (b) three pair of genes
In simple words: Human traits like height and skin color are examples of polygenic inheritance, meaning they are controlled by several genes working together, not just one or two. It is known that about three pairs of genes contribute to these traits.

🎯 Exam Tip: Remember that polygenic traits show continuous variation (a range of phenotypes) because they are influenced by multiple genes and often environmental factors too.

 

Question 52. The genotypic ratio of monohybrid cross is
a. 3:1
b. 1:2:1
c. 3:1:1
d. 9:3:3:1
Answer: (b) 1:2:1
In simple words: In a monohybrid cross, when you look at the genes (genotype) of the offspring, you'll typically find a ratio of 1 homozygous dominant, 2 heterozygous, and 1 homozygous recessive. This is expressed as 1:2:1.

🎯 Exam Tip: Be careful to distinguish between phenotypic ratio (what you see, e.g., 3 tall: 1 dwarf) and genotypic ratio (the actual gene combinations, e.g., 1 TT: 2 Tt: 1 tt) for a monohybrid cross.

 

Question 53. Which of the following statements are true regarding law of segregation
a. alleles separate with each other during gametogenesis
b. The segregation of factors is due to the segregation of chromosomes during meiosis
c. Law of segregation is called as law of purity of gametes
d. All of the options
Answer: (d) All of the options
In simple words: The Law of Segregation states that during the formation of gametes (sperm or egg cells), the two alleles for each trait separate from each other, ensuring each gamete receives only one allele. This separation happens because homologous chromosomes move apart during meiosis.

🎯 Exam Tip: The Law of Segregation is a cornerstone of Mendelian genetics; understanding its basis in meiosis and its implication for gamete purity is essential.

 

Question 54. The crossing of F1 to anyone of the parents is called
a. test cross
b. back cross
c. Fl cross
d. All of the options
Answer: (b) back cross
In simple words: A back cross is when a hybrid organism (F1 generation) is mated with one of its parent genotypes. This can be used in breeding programs to introduce traits from a wild variety into a cultivated one.

🎯 Exam Tip: While all test crosses are back crosses, not all back crosses are test crosses. A test cross specifically involves crossing the F1 hybrid with a *recessive* parent to determine the F1's genotype.

 

Question 55. The character that is express in to the F2 is called
a. recessive character
b. co-dominant character
c. dominant character
d. None of the options
Answer: (c) dominant character
In simple words: In Mendel's experiments, the trait that appears in the F1 generation and then again in the F2 generation in a larger proportion is the dominant character. It masks the recessive character.

🎯 Exam Tip: Dominant characters are those that are expressed when at least one dominant allele is present, which is why they show up in the F1 generation of a monohybrid cross.

 

Question 56. The recessive character will express in
a. F₁
b. F2
c. both a & b
d. F3 only
Answer: (b) F2
In simple words: A recessive character only appears when two copies of the recessive allele are present. In a monohybrid cross, this happens in the F2 generation (after F1 individuals self-pollinate), where it reappears in a 1:3 ratio with the dominant character.

🎯 Exam Tip: Remember that recessive traits are hidden in the F1 generation if the parents are pure dominant and pure recessive, but they always reappear in the F2 generation.

 

Question 57. Which of the following pair is not correct
a. KK=dominant
b. hybrid = heterogeneous
c. heterozygous = Kk
d. homozygous = Rr
Answer: (a) KK=dominant
In simple words: The pairing 'KK=dominant' is not entirely correct. 'KK' represents a homozygous dominant genotype, which *expresses* a dominant phenotype. The term 'dominant' itself refers to the allele or the phenotype, not the genotype in isolation. The option given as the answer (a) has a small typo 'dominat'.

🎯 Exam Tip: Be precise with genetic terminology. 'Dominant' usually refers to the allele or the expressed trait, while 'homozygous dominant' describes the specific genotype (e.g., KK, TT).

 

Question 58. Some genes have allele that prevents survival when homozygous or heterozygous. What is the kind of allele?
Answer: The kind of allele that prevents survival when an organism is homozygous or heterozygous for it is called a lethal allele. These alleles can cause death at different stages, from embryonic to adult.
In simple words: An allele that causes an organism to die is called a lethal allele.

🎯 Exam Tip: Lethal alleles are important because they can affect population genetics and lead to specific phenotypic ratios that deviate from standard Mendelian inheritance patterns.

 

Question 59. Mendel worked at the rules of inheritance and arrived at the correct mechanism. But
a. without any knowledge of cellular mechanism
b. knowledge of cellular mechanism
c. heredity mechanism
d. growth mechanism
Answer: (a) without any knowledge of cellular mechanism
In simple words: Mendel discovered the basic rules of how traits are passed down without knowing about DNA, chromosomes, or how cells divide. His work was remarkable because he figured out these complex ideas just by observing pea plants.

🎯 Exam Tip: It's incredible that Mendel deduced the fundamental laws of heredity purely from experimental crosses and statistical analysis, long before the cellular and molecular basis of genetics was understood.

 

Question 60. is crossing an individual of unknown one pair of a genes is called genetic genotype with a homozygous recessive.
a. back cross
b. test cross
c. monohybrid cross
d. dihybrid cross
Answer: (b) test cross
In simple words: A test cross is done to figure out the unknown genetic makeup (genotype) of an individual that shows a dominant trait. This is achieved by crossing it with an individual that is homozygous recessive for that trait.

🎯 Exam Tip: The key feature of a test cross is using a homozygous recessive parent, which ensures that its alleles will not mask any alleles from the unknown parent, making the F1 phenotype directly reflect the unknown genotype.

IX. One Mark Question

 

Question 1. The genetic constitution of the individual is called
Answer: The genetic constitution of an individual is called its genotype. This includes all the genes and alleles an organism possesses.
In simple words: An individual's complete set of genes is called its genotype.

🎯 Exam Tip: Always distinguish between 'genotype' (the genetic makeup) and 'phenotype' (the observable characteristics) in genetics questions.

IX. One Mark Question

 

Question 1. The genetic constitution of the individual is called
Answer: Genotype
In simple words: The genotype is the full set of genes an organism has, which tells us what traits it might show.

🎯 Exam Tip: Remember that "genotype" refers to the genetic makeup, while "phenotype" refers to the observable physical traits.

 

Question 2. The observable characteristics of an organism are called
Answer: Phenotype
In simple words: A phenotype is how an organism looks or behaves because of its genes and environment, like its color or height.

🎯 Exam Tip: Phenotype is what you can see, hear, or measure, like hair color or disease symptoms, which helps in identifying genetic expressions.

 

Question 3. Who is father of genetics?
Answer: Gregor Johann Mendel
In simple words: Gregor Mendel is known as the father of genetics because he was the first to discover how traits are passed from parents to children through his pea plant experiments.

🎯 Exam Tip: Always remember Gregor Mendel's full name, as it's a key term in genetics.

 

Question 4. Name the Mendel's published work.
Answer: Experiments on Plant Hybrids.
In simple words: Mendel's famous paper, called "Experiments on Plant Hybrids," explained his findings about how traits are passed down in pea plants.

🎯 Exam Tip: Knowing the title of Mendel's work helps contextualize his significant contributions to genetics.

 

Question 5. Name the publication of Mendel research work
Answer: The proceedings of the Brunn Society & Natural History.
In simple words: Mendel's research paper was published in a scientific journal from a society in Brunn, called "The Proceedings of the Brunn Society & Natural History".

🎯 Exam Tip: This specific publication is important to remember as it was the venue where Mendel's groundbreaking genetic research was first shared with the scientific community.

 

Question 6. What is the year of published work Mendel's Research paper?
Answer: The proceedings of the Brunn Society & Natural History.
In simple words: Mendel's research paper, which explained how traits are passed on, was published in a journal called "The Proceedings of the Brunn Society & Natural History". His work was published in 1866.

🎯 Exam Tip: It is crucial to remember the publication's name along with the year (1866) for historical accuracy in genetics.

 

Question 7. What is an allele?
Answer: It is another word for a Gene.
In simple words: An allele is a version of a gene, like how a gene for eye color can have alleles for blue or brown eyes.

🎯 Exam Tip: Clearly differentiate between a gene (a segment of DNA coding for a trait) and an allele (a specific form of that gene).

 

Question 8. Individuals show a range of traits with small difference between them.
Answer: Continuous variation
In simple words: Continuous variation is when traits, like height, show a smooth range of differences among individuals, not just distinct categories.

🎯 Exam Tip: Continuous variation is often influenced by multiple genes and environmental factors, leading to a spectrum of phenotypes.

 

Question 9. When an individual show two or a few traits with large differences between them. This type of variation is called.
Answer: Discontinuous variation
In simple words: Discontinuous variation is when traits fall into clear, separate groups with big differences, like having either red or white flowers, with nothing in between.

🎯 Exam Tip: Discontinuous variation is typically controlled by one or a few genes and is not significantly affected by the environment.

 

Question 10. Human height is the good example of .............. variation.
Answer: Continuous variation
In simple words: Human height is a good example of continuous variation because people have many different heights, not just a few set ones.

🎯 Exam Tip: Remember that continuous variation usually produces a bell-shaped curve when plotted, showing a wide range of values.

 

Question 11. Human skin colour is the good example of .............. variation.
Answer: Continuous variation
In simple words: Human skin color is a great example of continuous variation, as there's a wide range of shades, not just a few distinct categories.

🎯 Exam Tip: Traits like skin color, influenced by many genes, illustrate polygenic inheritance and continuous variation.

 

Question 12. Mention any two examples of continuous variation.
Answer: Human height and human skin colour.
In simple words: Two examples of continuous variation, where traits show a wide range, are human height and human skin color.

🎯 Exam Tip: When providing examples, choose traits that can be measured on a scale rather than counted in distinct categories.

 

Question 13. Mention any two examples of discontinuous variation.
Answer: Style length of Primula & Height of the garden pea.
In simple words: Two examples of discontinuous variation, where traits fall into clear separate groups, are the style length of Primula flowers and the height (tall or dwarf) of garden pea plants.

🎯 Exam Tip: Discontinuous variation often involves traits with distinct categories, such as blood groups or flower colors (red, white, pink).

 

Question 14. A trait that makes the expression of another trait when both version of the gene are present in the individual called
Answer: Dominant.
In simple words: A dominant trait is one that shows up in an individual, even if there's only one copy of the gene for it, hiding the other trait.

🎯 Exam Tip: Always remember that a dominant allele expresses its phenotype even in the presence of a recessive allele.

 

Question 15. What is F₁?
Answer: It is the first filial generation in a cross; the offspring of the parental generation.
In simple words: F₁ stands for the "first generation offspring," which are the children resulting from the first cross between two parents.

🎯 Exam Tip: Understand the sequence: Parental (P) generation cross produces the F1 generation, and F1 self-crossing produces the F2 generation.

 

Question 16. The letter 'P' denoted in genetics is
Answer: The parental generation in a cross.
In simple words: In genetics, 'P' refers to the parent generation, which are the original organisms that are crossed in an experiment.

🎯 Exam Tip: Clarify that the 'P' generation represents the initial set of individuals used in a genetic cross.

 

Question 17. A variation in an inherited characteristics is
Answer: Trait
In simple words: A trait is a specific quality or characteristic that an organism can inherit from its parents, like hair color or plant height.

🎯 Exam Tip: Traits are the observable features or characteristics that genetics studies, distinguishing individuals within a species.

 

Question 18. One pair genes can completely makes the expression of another pair of genes known as
Answer: Epistasis
In simple words: Epistasis is when one gene's effect completely covers up or changes the way another gene shows its trait.

🎯 Exam Tip: Epistasis is a form of gene interaction where one gene modifies the phenotypic expression of another gene at a different locus.

 

Question 19. Who discovered incomplete dominance?
Answer: Correns. (Germany)
In simple words: Carl Correns, a scientist from Germany, discovered incomplete dominance, where two traits blend together instead of one completely hiding the other.

🎯 Exam Tip: Remember that Carl Correns was one of the three scientists who independently rediscovered Mendel's laws and also found incomplete dominance.

 

Question 20. Crosses between F₁ offsprings with either of the two parents (hybrids) are known as
Answer: Back cross
In simple words: A back cross is when a hybrid offspring (F₁) is mated back with one of its parent types.

🎯 Exam Tip: A back cross is useful for producing offspring that are genetically closer to one of the parents or for identifying heterozygotes.

 

Question 21. Diploid organisms that have two different allele at a specific gene locus are said to be
Answer: Heterozygous
In simple words: When an organism has two different versions of a gene for a trait, it is called heterozygous for that trait.

🎯 Exam Tip: Understand that heterozygous means having two different alleles (e.g., Aa), while homozygous means having two identical alleles (e.g., AA or aa).

 

Question 22. TT referred as...................
Answer: Homozygous dominant variety.
In simple words: "TT" describes an organism that has two identical dominant genes for a trait, meaning it's pure for that dominant characteristic.

🎯 Exam Tip: Capital letters (like T) usually represent dominant alleles, and two identical capital letters (TT) denote a homozygous dominant genotype.

 

Question 23. ‘tt' referred as ...................
Answer: Homozygous recessive character.
In simple words: "tt" means an organism has two identical recessive genes for a trait, showing the recessive characteristic.

🎯 Exam Tip: Small letters (like t) represent recessive alleles, and two identical small letters (tt) denote a homozygous recessive genotype.

 

Question 24. 'Tt' denotes for ..................
Answer: Heterogeneous hybrid variety.
In simple words: "Tt" describes an organism that has one dominant gene and one recessive gene for a trait, making it a mixed or hybrid type.

🎯 Exam Tip: The term "heterozygous" or "hybrid" indicates the presence of two different alleles for a specific trait.

 

Question 25. The superiority of hybrid over either of its parents in one or more traits known as
Answer: Hybrid vigour or Heterosis
In simple words: Hybrid vigour, or heterosis, is when hybrid offspring are stronger, healthier, or grow better than either of their purebred parents.

🎯 Exam Tip: Hybrid vigour is often seen in agriculture, where crossing different pure lines produces more productive crops or livestock.

 

Question 26. The site or position of a particular gene on a chromosome is
Answer: locus
In simple words: The locus is the exact spot on a chromosome where a specific gene is located.

🎯 Exam Tip: Understanding "locus" is fundamental to gene mapping and identifying where genetic traits reside.

 

Question 27. An allele which has the potential to cause the death of an organism is called
Answer: Lethal genes
In simple words: Lethal genes are special genes that can cause an organism to die, sometimes even before it's born.

🎯 Exam Tip: Lethal alleles can be dominant or recessive, and their effect may vary depending on whether the organism is homozygous or heterozygous for the allele.

 

Question 28. A single gene affects multiple traits are called
Answer: Pleiotropy
In simple words: Pleiotropy is when one single gene influences many different traits or characteristics in an organism.

🎯 Exam Tip: Marfan syndrome is a classic example of pleiotropy, where a single gene mutation affects the heart, eyes, and bones.

 

Question 29. A single gene affects multiple traits and alter the phenotype of the organism is
Answer: Pleiotropy
In simple words: Pleiotropy is when one gene has an impact on several different traits, changing how an organism looks or functions in many ways.

🎯 Exam Tip: Identify pleiotropy when a single genetic change leads to a range of seemingly unrelated symptoms or characteristics.

 

Question 30. Several genes combine to affect a single trait of an organism. This kind of inheritance is
Answer: Polygenic inheritance.
In simple words: Polygenic inheritance happens when many different genes work together to control just one trait, like human height or skin color.

🎯 Exam Tip: Polygenic traits often show continuous variation, resulting in a wide range of phenotypes rather than distinct categories.

 

Question 31. Who demonstrated first experiment on polygenic inheritance.
Answer: Swedish Geneticist H. Nilsson – Ehle (1909)
In simple words: H. Nilsson-Ehle, a Swedish geneticist, was the first to show how many genes can work together to control one trait through his wheat kernel color experiments in 1909.

🎯 Exam Tip: Remembering Nilsson-Ehle's work on wheat kernel color helps illustrate the concept of polygenic inheritance and its historical discovery.

 

Question 32. Which plant to use to identify the polygenic inheritance?
Answer: Wheat - Kernel colour (dark red & white variety)
In simple words: Wheat was used to study polygenic inheritance, specifically looking at the different shades of kernel color, from dark red to white.

🎯 Exam Tip: Wheat kernel color provided a clear visual example of how multiple genes contribute to a continuous spectrum of a single trait.

 

Question 33. List any two intragenic or allele interaction.
Answer:
1. Incomplete Dominance
2. Co-dominance
In simple words: Two ways genes interact within the same gene pair are incomplete dominance, where traits blend, and co-dominance, where both traits show up fully.

🎯 Exam Tip: These interactions show that Mendelian inheritance patterns are not always simple dominant-recessive relationships.

 

Question 34. List any two intergenic or non-allele interaction
Answer:
1. Dominant Epistasis
2. Recessive Epistasis
In simple words: Two types of gene interaction between different genes are dominant epistasis, where one gene hides another's effect, and recessive epistasis, where a recessive gene hides another's effect.

🎯 Exam Tip: Intergenic interactions involve genes at different loci influencing a single trait, leading to modified Mendelian ratios.

 

Question 35. Corren has used plant for studied incomplete dominance.
Answer: Mirabilis jalapa (4' O clock plant)
In simple words: Carl Correns used the Mirabilis jalapa, also known as the 4 o'clock plant, to discover incomplete dominance, where red and white flowers produce pink ones.

🎯 Exam Tip: The 4 o'clock plant is a classic example in genetics for demonstrating how traits can blend, showing an intermediate phenotype.

 

Question 36. Mention the botanical name of 4' O clock plant.
Answer: Mirabilis jalapa.
In simple words: The scientific name for the 4 o'clock plant, famous for showing incomplete dominance, is Mirabilis jalapa.

🎯 Exam Tip: Always use proper capitalization (genus capitalized, species lowercase) and italicization for botanical names.

 

Question 37. Duplicate genes with cumulative effect of non-allelic interaction is derived in
Answer: Fruit shape in Summer squash.
In simple words: The fruit shape in summer squash is an example of how duplicate genes, when working together, create combined effects.

🎯 Exam Tip: Duplicate genes often result in modified F2 phenotypic ratios, such as 15:1, where multiple dominant alleles lead to the same phenotype.

 

Question 38. What is the F₁ phenotypic ratio of inhibitor genes in the intergenic interaction?
Answer: 13:3
In simple words: When inhibitor genes interact between different gene pairs, the F₁ generation often shows a phenotypic ratio of 13:3, meaning 13 parts of one trait and 3 parts of another.

🎯 Exam Tip: Inhibitor genes suppress the expression of other genes, often resulting in unique phenotypic ratios that deviate from standard Mendelian ratios.

 

Question 39. When the heterozygote exhibits a mixture of phenotypic character of both homozygous called as
Answer: Co-Dominance.
In simple words: Co-dominance is when both versions of a gene show their traits completely and at the same time in a heterozygous organism, instead of one hiding the other.

🎯 Exam Tip: A classic example of co-dominance is the ABO blood group system, where both A and B alleles are expressed simultaneously in AB blood type.

 

Question 40. Name the two gene interaction.
Answer:
1. Intralocus interaction (allelic interaction)
2. Interlocus interaction (non-allelic interaction)
In simple words: Genes can interact in two main ways: either within the same gene pair (intralocus) or between different gene pairs (interlocus).

🎯 Exam Tip: Intralocus interactions refer to how different alleles of the same gene behave, while interlocus interactions describe how different genes influence each other.

 

Question 41. A chart shows which genes are co-dominant. This is known as
Answer: A pedigree charts.
In simple words: A pedigree chart is a family tree-like diagram that shows how traits, including co-dominant ones, are passed down through generations.

🎯 Exam Tip: Pedigree charts are essential tools for tracking genetic disorders and predicting inheritance patterns within families.

 

Question 42. Each character is controlled by distinct units called factor, which occur in pairs. If the pairs are heterozygous, one wiil always dominant other. This is known as
Answer: First law of inheritance or Law of Dominance.
In simple words: This describes Mendel's First Law, or the Law of Dominance, stating that when two different gene versions are present, one (dominant) will show up, while the other (recessive) will be hidden.

🎯 Exam Tip: The Law of Dominance explains why certain traits appear in the F1 generation while others remain masked, only reappearing in later generations.

 

Question 43. The second law of inheritance otherwise called as
Answer: Law of Segregation.
In simple words: Mendel's second law, the Law of Segregation, says that the two copies of each gene separate during gamete formation, so each parent passes on only one copy to their offspring.

🎯 Exam Tip: The Law of Segregation ensures that each gamete (sperm or egg) receives only one allele for each gene, explaining how genetic variation is maintained.

 

Question 44. Give the name of the scientists who re-discovered Mendelism
Answer:
1. Hugo Devries
2. Carl Correns
3. Erich Von Tschermak.
In simple words: Three scientists, Hugo de Vries, Carl Correns, and Erich von Tschermak, independently rediscovered Mendel's laws of inheritance many years after his initial work.

🎯 Exam Tip: These three scientists' independent discoveries confirmed the universal applicability of Mendel's principles of heredity.

 

Question 45. is the prerequisite for Hybridization technique.
Answer: Emasculation.
In simple words: Emasculation, which is removing the male parts of a flower, is a necessary step before hybridization to prevent self-pollination.

🎯 Exam Tip: Emasculation ensures controlled cross-pollination, allowing breeders to study specific genetic crosses accurately.

 

Question 46. Transmission of genes that occur outside the nucleus is called....................
Answer: Cytoplasmic Inheritance or Extra Nuclear
In simple words: When genes are passed down outside of the cell's nucleus, like from mitochondria or chloroplasts, it's called cytoplasmic inheritance.

🎯 Exam Tip: Cytoplasmic inheritance is often maternal, meaning the offspring inherit these traits primarily from the mother's cytoplasm.

 

Question 47. Cytoplasmic inheritance are found in
Answer: Mitochondria & Chloroplast
In simple words: Genes for cytoplasmic inheritance are located in the mitochondria and chloroplasts, which are organelles outside the cell nucleus.

🎯 Exam Tip: Both mitochondria and chloroplasts have their own small circular DNA, which is distinct from the nuclear DNA and passed down independently.

 

Question 48. The interaction between separate gene in which one makes the effect of another
Answer: Epistasis
In simple words: Epistasis is a genetic event where one gene changes or hides the effect of another gene that is located at a different position.

🎯 Exam Tip: Epistasis is crucial for understanding complex traits where multiple genes contribute to a single phenotype.

 

Question 49. The acquisition of traits or conditions controlled by self replicating substances within the cytoplasm. This is a type of
Answer: Cytoplasmic Inheritance.
In simple words: This describes cytoplasmic inheritance, where traits are passed on through self-replicating materials found in the cell's cytoplasm, not just the nucleus.

🎯 Exam Tip: Traits controlled by cytoplasmic inheritance show unique patterns, often differing from Mendelian inheritance, and are typically inherited maternally.

 

Question 50. The hybrid progeny in the first generation is called as
Answer: F1
In simple words: The first generation of hybrid offspring from a cross is called the F1 generation.

🎯 Exam Tip: The F1 generation is always the direct result of crossing two parental (P) individuals.

 

Question 51. The innate tendency of offspring to resemble their parents is called
Answer: Heredity
In simple words: Heredity is the natural process by which children receive traits and characteristics from their parents.

🎯 Exam Tip: Heredity explains why family members often share similar physical features, behaviors, or predispositions to certain conditions.

 

Question 52. The tendency of offspring to differ from parents is called
Answer: Variation
In simple words: Variation is the natural differences that exist among offspring, making them not exactly identical to their parents.

🎯 Exam Tip: Variation is essential for evolution, as it provides the raw material for natural selection to act upon.

 

Question 53. Multiple allelic inheritances is otherwise called as
Answer: Co-dominance
In simple words: When there are many different versions (alleles) of a gene, and more than two alleles exist in a population, this is known as multiple allelic inheritance.

🎯 Exam Tip: The ABO blood group system in humans is a prime example of multiple alleles, where three alleles (A, B, O) determine four blood types.

 

Question 54. What is the use of pedigree analysis in genetics?
Answer: It helps in genetic counselling.
In simple words: Pedigree analysis helps genetic counselors understand how traits or diseases are passed down in families, providing important information for advice.

🎯 Exam Tip: Pedigree charts are valuable for identifying inheritance patterns (e.g., autosomal dominant, recessive, X-linked) and assessing risks for future generations.

 

Question 55. Who proposed the genetic theory of inheritance?
Answer: T.H.Morgan
In simple words: T.H. Morgan, or Thomas Hunt Morgan, proposed the genetic theory of inheritance, showing that genes are located on chromosomes and are the units of heredity.

🎯 Exam Tip: Morgan's work with fruit flies (Drosophila) provided crucial evidence for the chromosomal theory of inheritance, building upon Mendel's foundational work.

 

Question 56. Give one good example for Atavism in plants.
Answer: Reemergence of sexual reproduction in Hieracium pilosella.
In simple words: A plant called Hieracium pilosella showing sexual reproduction again, after having lost it, is a good example of atavism.

🎯 Exam Tip: Atavism illustrates the persistence of genetic potential for ancestral traits that may reappear under specific conditions.

 

Question 17. What are multiple alleles?
Answer: Alleles are alternative forms of a gene, and they are responsible for differences in how a trait appears. If a gene has at least two different forms, it is called polymorphic. When a particular gene exists in three or more different forms, these are known as multiple alleles. This increases the variety of traits observed.
In simple words: Multiple alleles mean a gene has more than two possible forms. These different forms lead to different ways a trait can show up.

🎯 Exam Tip: Remember that multiple alleles increase the variety of traits seen in a population for a single gene.

 

Question 18. Briefly explain Mendelian Genetics.
Answer: Mendelian genetics refers to the theories and principles discovered by Gregor Mendel. These theories explain the inheritance pattern of genetic characteristics based on simple breeding experiments. He studied how single genes located on chromosome pairs are passed down from parents to offspring. His work laid the foundation for modern genetics.
In simple words: Mendelian genetics explains how parents pass traits to their children. It uses Mendel's rules about single genes on chromosomes.

🎯 Exam Tip: Focus on Mendel's key principles like dominance, segregation, and independent assortment when explaining Mendelian genetics.

 

Question 19. Write a note on Gene interaction.
Answer: Gene interaction is a phenomenon where a single phenotype is controlled by more than one set of genes. Each of these gene sets can have two or more alleles. This means that the expression of one gene can influence or modify the expression of another gene, leading to complex inheritance patterns. It shows that traits are often not determined by a single gene alone.
In simple words: Gene interaction means many genes work together to create one trait. Each gene can have different forms that change how the trait looks.

🎯 Exam Tip: Gene interaction shows that inheritance is often more complex than a single gene controlling a single trait.

 

Question 20. Explain the three kinds of plants that have recessive lethal gene in Antirrhinum sp.
Answer: In Antirrhinum plants, a recessive lethal gene can lead to three different kinds of plants: 1. Green plants with chlorophyll (CC): These plants are healthy and produce their own food. 2. Yellowish-green plants with carotenoids (Cc): These plants have less chlorophyll and appear pale green or golden. 3. White plants without any chlorophyll (cc): These plants cannot survive for long because they cannot make their own food through photosynthesis. The lack of chlorophyll is a fatal trait.
In simple words: In Antirrhinum plants, some genes can cause plants to be green, yellowish-green, or white. The white plants cannot live because they don't have the green color (chlorophyll) they need to grow.

🎯 Exam Tip: Understand that lethal genes can cause death at different stages of development, and in this case, it's due to the absence of a vital pigment.

 

Question 21. Write a note on incomplete dominance.
Answer: Incomplete dominance is a genetic situation where neither of the alleles for a trait completely dominates the other. Instead, when both alleles are present in a heterozygote, they combine to produce an intermediate phenotype. This means the expressed physical trait is a blend of the phenotypes of both alleles. For example, crossing a red flower with a white flower might produce pink flowers. The new trait is a mix of the two parent traits.
In simple words: In incomplete dominance, two different traits mix together to make a new, in-between trait. Neither of the original traits fully wins.

🎯 Exam Tip: Remember that incomplete dominance creates an intermediate phenotype, unlike codominance where both traits are fully expressed.

 

Question 22. A diagram that shows the possible outcomes of breeding between two individuals.
Answer: The diagram that shows the possible outcomes of breeding between two individuals is called a Punnett square or checkerboard. It is a graphical representation used in genetics to predict the genotypes and phenotypes of offspring from a cross. It systematically lists all possible combinations of alleles from the parents.
In simple words: A Punnett square is a drawing that helps us see all the possible types of babies two parents could have.

🎯 Exam Tip: Practicing drawing Punnett squares for different crosses helps visualize genetic outcomes clearly.

 

Question 23. Write a note on Punnet Square.
Answer: A Punnett Square is a square diagram used in genetics to predict the genotypes of offspring from a cross. It is a cross-multiplication matrix where the gametes (sex cells) of one parent are listed along the top, and the gametes of the other parent are listed along the side. The squares inside show all the possible gene combinations and their probabilities for the offspring. It makes visualizing genetic crosses easy.
In simple words: A Punnett Square is a special drawing to show all the possible ways genes can mix from two parents. It helps predict what their children might look like.

🎯 Exam Tip: The Punnett Square is a visual tool to calculate the probability of different genetic combinations, showing all potential allele pairings.

 

Question 24. What do you mean by genetics ?
Answer: Genetics is the branch of biological science that studies the process of heredity. It deals with how living things receive common traits from previous generations. This field explores genes, genetic variation, and the mechanisms by which characteristics are passed from parents to offspring. It helps us understand the fundamental rules of life's continuity.
In simple words: Genetics is the study of how living things get traits from their parents. It helps us understand why we look like our family.

🎯 Exam Tip: When defining genetics, highlight "heredity" and "transmission of traits" as key concepts.

 

Question 25. What are genes ?
Answer: Genes are the fundamental functional units of inheritance. They are the basic units of heredity, carrying biological information. Genes transmit biochemical, anatomical, and behavioral traits from parents to their offspring. Each gene is typically made up of a sequence of DNA that codes for a specific product, like a protein. Genes are essential for defining all characteristics of an organism.
In simple words: Genes are like small instruction books inside us that tell our bodies what to be like, passed down from our parents.

🎯 Exam Tip: Emphasize that genes are the "units of inheritance" and carry "biological information" in the form of DNA.

 

Question 26. What is population Genetics ?
Answer: Population genetics is the study of heredity in groups of individuals, rather than just pairs of parents. It looks at how genetic variation exists within a population and how the frequencies of genes and alleles change over time. This field examines and models these changes across different geographic areas and periods, helping to understand evolution.
In simple words: Population genetics studies how genes behave in large groups of living things. It looks at how gene amounts change over time in a population.

🎯 Exam Tip: Key terms for population genetics are "gene frequencies," "allele frequencies," and "changes over time."

 

Question 27. Define Molecular genetics.
Answer: Molecular genetics is a field of biology that specifically studies the structure and function of genes at a molecular level. It focuses on how genetic material, primarily DNA and RNA, works to control cell activities and inherited traits. This branch examines the details of gene expression, replication, and repair, along with interactions between genes and other cellular molecules.
In simple words: Molecular genetics studies genes very closely, looking at what they are made of and exactly how they work inside cells.

🎯 Exam Tip: Highlight "molecular level" and "structure and function of genes" in your definition.

 

Question 29. What do you mean by genetic transmission ?
Answer: Genetic transmission refers to the transfer of genetic information from parents to their offspring. It is almost synonymous with heredity and describes the fundamental process by which traits and characteristics are passed down through generations. This process ensures the continuity of genetic material and the persistence of species-specific traits.
In simple words: Genetic transmission is simply how genes and traits are given from parents to their children.

🎯 Exam Tip: Link "genetic transmission" directly to the "transfer of genetic information" between generations.

 

Question 30. Define Transmission Genetics :
Answer: Transmission genetics is the study of the mechanisms involved in the passage of genes from one generation to the next. It focuses on the patterns of inheritance and how traits are passed down within families. This field uses techniques like Mendelian crosses and pedigree analysis to understand these patterns.
In simple words: Transmission genetics is the study of how traits and genes are passed down from one generation to the next.

🎯 Exam Tip: This term focuses on the "mechanism" of heredity, explaining the process of trait transfer.

 

Question 31. What are polygenes ?
Answer: Polygenes are genes where the individual effect on a phenotype is too small to be easily seen. However, they work together with other polygenes to produce observable variation in a trait. These genes are also called multiple factors and often have additive or cumulative effects, meaning each gene adds a small amount to the trait. A good example is human skin color, which is determined by several polygenes.
In simple words: Polygenes are many small genes that work together to create one big trait, like skin color. Each gene adds a little bit to the final look.

🎯 Exam Tip: Remember that polygenes lead to continuous variation, where traits show a range of possibilities rather than distinct categories.

 

Question 33. Mendel was successful, why?
Answer: Mendel was successful in his breeding experiments for a few key reasons:

• He applied mathematical and statistical methods, including the laws of probability, to analyze his breeding experiments.
• He carefully used pairs of contrasting characters in his experiments, which made it easier to observe specific inheritance patterns.

These systematic approaches helped him discover the fundamental rules of heredity.
In simple words: Mendel succeeded because he used math to understand his results and picked clear, different traits to study.

🎯 Exam Tip: Mentioning Mendel's use of mathematics and discrete, contrasting traits are crucial for explaining his success.

 

Question 34. Write a note on self fertization.
Answer: Self-fertilization is a process where the male and female gametes (sex cells) produced by the *same individual* fuse together. In plants, this is often called self-pollination. This process occurs in many protozoans and invertebrate animals as well. It allows a single, isolated organism to reproduce, but it limits the genetic diversity of the offspring compared to cross-fertilization. The seeds produced through self-fertilization are genetically very similar to the parent.
In simple words: Self-fertilization is when one living thing's male and female parts join together to make a new one. It's like a plant pollinating itself, which makes new plants but with less variety.

🎯 Exam Tip: For full marks, explain that self-fertilization involves gametes from the "same individual" and note its effect on genetic diversity.

 

Question 35. What is cross fertilisation ?
Answer: Cross-fertilization is a type of sexual reproduction where the fusion of male and female gametes comes from *different individuals* of the same species. It is also known as allogamy. This process commonly occurs in dioecious plants and in animal species where male and female individuals are separate. Cross-fertilization increases genetic variation and adaptability in a population, which is important for evolution.
In simple words: Cross-fertilization is when two different living things of the same kind join their sex cells to make a new one. This creates offspring with more varied traits.

🎯 Exam Tip: Emphasize that cross-fertilization involves gametes from "different individuals" and contributes to "genetic diversity."

 

Question 36. Does pure breeding means homozygous?
Answer: Yes, pure breeding means that the individuals are homozygous for the traits being studied. This implies they have identical alleles (e.g., TT or tt) for a specific gene. A group of pure-breeding individuals will consistently produce offspring with the same phenotype when intercrossed or self-pollinated, demonstrating stable inheritance.
In simple words: Yes, pure breeding means an animal or plant has matching genes for a trait (homozygous) and will always have babies that look the same for that trait.

🎯 Exam Tip: Clearly state "yes" and connect "pure breeding" to "homozygous" and "consistent offspring phenotype."

 

Question 37. What is the relationship between pure breeding and true breeding ?
Answer: Pure breeding and true breeding are synonymous terms in genetics. They both refer to organisms that consistently produce offspring with the same traits as themselves, across many generations, when self-fertilized or intercrossed. This consistency arises because these organisms possess a pure genotype (are homozygous) for the traits being considered. For example, a true-breeding tall plant will always produce tall offspring.
In simple words: Pure breeding and true breeding mean the exact same thing. It's when a plant or animal always passes down the same trait to its babies, like always having red flowers.

🎯 Exam Tip: State clearly that the terms are synonymous and explain the consistent inheritance of traits.

 

Question 38. Write a short note on Anthocyanin pigment.
Answer: Anthocyanins are naturally occurring pigments that give plants their red, purple, and blue colors. These pigments are more stable and appear red in acidic conditions (low pH). If the pH value is higher, the color of anthocyanin can shift towards blue or purple. They play a vital role in attracting pollinators, protecting plants from UV damage, and acting as antioxidants. They add beautiful colors to flowers and fruits.
In simple words: Anthocyanin is a natural color that makes plants red, purple, or blue. It changes color based on how acidic or basic the plant is.

🎯 Exam Tip: Mention the colors produced by anthocyanin and how pH affects its stability and color expression.

 

Question 39. What is the mean 'progeny'?
Answer: The word 'progeny' comes from the Latin verb "progignere," which means "to beget." In biology, progeny refers to the young or offspring born from a living organism. These can be produced either by a single organism (asexual reproduction) or through sexual reproduction. The collective offspring of animals or plants can also be referred to as a brood or the children of a species.
In simple words: 'Progeny' simply means the children or offspring born from an animal or plant.

🎯 Exam Tip: Define "progeny" as offspring and mention its Latin origin if you want to add an extra detail.

 

Question 40. Point out the mechanism of Trihybird cross.
Answer: A trihybrid cross involves breeding two individuals that differ in three distinct genetic traits. For example, crossing pure tall, yellow, round plants (TTYYRR) with pure dwarf, green, wrinkled plants (ttyy rr). If the \(F_1\) generation is self-fertilized, it can produce 8 different types of gametes, leading to 64 possible zygote combinations. This cross follows Mendel's laws of segregation and independent assortment. The \(F_2\) phenotypic ratio for a trihybrid cross is \(27:9:9:9:3:3:3:1\), showing a wide array of combinations for the three traits.
In simple words: A trihybrid cross means looking at three different traits at the same time when breeding plants. It's a bit complex because many different combinations can happen.

🎯 Exam Tip: Mentioning that Mendel's laws apply and quoting the \(27:9:9:9:3:3:3:1\) \(F_2\) phenotypic ratio is key for trihybrid crosses.

 

Question 41. What is back cross ?
Answer: A back cross is a genetic cross where an \(F_1\) offspring (a hybrid) is bred with one of its two parental genotypes. The parent used for the cross can be either the dominant or the recessive parent. If \(F_1\) individuals are crossed with a true-breeding parent from which they were derived, this cross is called a back cross. For instance, if \(F_1\) generation (Tt) from a TT x tt cross is bred with either TT or tt, it's a back cross. This method helps maintain desirable parental traits.
In simple words: A back cross is when you cross a first-generation hybrid with one of its original parents. It helps bring back some parental traits.

🎯 Exam Tip: Clearly define a back cross as \(F_1\) generation crossed with *either* parent, emphasizing it's about checking parental traits.

 

Question 42. What are the classification of gene interactions?
Answer: Gene interactions are classified based on how alleles interact, either within the same gene or between different genes:

• **Intralocus (Intragenic) Gene Interactions:** These occur between alleles of the *same gene*. Examples include:
  • Incomplete dominance (e.g., pink flowers from red and white parents)
  • Codominance (e.g., AB blood type)
  • Multiple alleles (e.g., ABO blood groups)
  • Pleiotropic genes (one gene affecting multiple traits)
• **Interlocus (Non-allelic) Gene Interactions:** These occur between alleles of *different genes* located at different loci. Examples include epistasis and complementary gene action.

In simple words: Gene interactions are how different genes or different forms of the same gene work together. Some happen within one gene, like when traits mix. Others happen between different genes.

🎯 Exam Tip: Distinguish between "intragenic" (within the same gene) and "intergenic" (between different genes) interactions.

 

Question 43. Inheritance of chloroplast and mitochondria characters are non-mendelian pattern why?
Answer: The inheritance of chloroplast and mitochondrial characters follows a non-Mendelian pattern because their genes are located in the cytoplasm, outside the cell's nucleus. This is known as extrachromosomal or cytoplasmic inheritance. These organelles are usually inherited solely from the maternal parent (mother) because the egg cell contributes most of the cytoplasm and its organelles to the zygote, while the sperm contributes primarily the nucleus. Therefore, these traits do not segregate according to Mendel's laws.
In simple words: Chloroplast and mitochondria genes do not follow Mendel's rules because they are found outside the main cell nucleus. They usually come only from the mother, since her egg cell gives the baby most of its cell fluid.

🎯 Exam Tip: The key reasons for non-Mendelian inheritance of these organelles are their "extranuclear location" and "maternal inheritance."

 

Question 44. What is hybrids?
Answer: Hybrids are organisms that are produced from a genetic cross between two parents with different genotypes. They carry different alleles for one or more traits and are thus heterozygous. In Mendel's experiments, for example, the \(F_1\) generation resulting from a cross between true-breeding tall and dwarf plants were hybrids, as they were heterozygous (Tt) for the height gene. Hybrids often exhibit hybrid vigor, meaning they can be stronger or more resilient than their parents.
In simple words: Hybrids are offspring made by mixing two different kinds of parents. They often have traits from both sides.

🎯 Exam Tip: Define hybrids as organisms from a cross of "genetically different parents," often heterozygous.

 

Question 45. What is Dihybrid cross?
Answer: A dihybrid cross is a genetic cross that involves individuals differing in two distinct characters or traits. It studies the inheritance pattern of two separate genes, each with two alleles, simultaneously. For instance, crossing a plant with round, yellow seeds (RRYY) with one having wrinkled, green seeds (rryy). This type of cross helps demonstrate Mendel's Law of Independent Assortment, showing how different traits are inherited independently of each other.
In simple words: A dihybrid cross is a breeding experiment that looks at two different traits at the same time, like seed shape and seed color.

🎯 Exam Tip: Emphasize that a dihybrid cross involves "two distinct characters" and allows observation of independent assortment.

 

Question 2. What is the human ABO phenotype blood type based on?
Answer: The human ABO phenotype blood type is based on the presence or absence of specific antigens (A and B) on the surface of red blood cells. These antigens are determined by the A, B, and O genes. The O allele is recessive, meaning it is only expressed if two O alleles are present. However, the A and B alleles are codominant; if both are present, both A and B antigens are fully expressed, resulting in AB blood type. This system involves multiple alleles and codominance to create the four main blood groups: A, B, AB, and O.

In simple words: Our blood type, like A, B, AB, or O, depends on certain genes (A and B) found on our red blood cells. The O gene is weaker than A and B, but A and B are equally strong.

🎯 Exam Tip: Remember that ABO blood groups are an excellent example of multiple alleles and codominance, with A and B being codominant and O being recessive.

 

Question 3. Explain the Genetic inheritance of pattern of human blood system ?
Answer: The genetic inheritance pattern of the human ABO blood group system is quite interesting, involving multiple alleles and codominance. Each person inherits two alleles for blood type, one from each parent, choosing from A, B, or O. The A and B alleles are codominant, meaning that if an individual inherits both \(I^A\) and \(I^B\), both are fully expressed, resulting in AB blood type. The O allele (i) is recessive to both A and B. So, an individual with genotype \(I^A i\) will have type A blood, and one with \(I^B i\) will have type B blood. Only individuals with two O alleles (ii) will have type O blood. This system shows how diverse allele interactions determine a single trait.
In simple words: How we get our blood type (A, B, AB, O) is like a mix from our parents' genes. A and B genes are equally strong, while the O gene is weaker.

🎯 Exam Tip: To explain ABO inheritance, focus on the concepts of "multiple alleles," "codominance" (A and B), and "recessiveness" (O).

 

Question 4. In blood type co-dominance or incomplete dominance ?
Answer: In the human ABO blood group system, the inheritance pattern of A and B alleles is an excellent example of **codominance**. This means that when an individual inherits both the A allele and the B allele (\(I^A I^B\)), both traits (A antigens and B antigens) are fully and equally expressed on the red blood cell surface. This results in the AB blood type, where neither A nor B is dominant over the other, and no intermediate phenotype is formed. Incomplete dominance, in contrast, would result in a blend, like pink flowers from red and white parents, which is not the case for blood types.
In simple words: For blood types, it's codominance, not incomplete dominance. Codominance means if you have both A and B genes, both show up completely, giving you AB blood.

🎯 Exam Tip: Distinguish codominance (both traits fully expressed, e.g., AB blood type) from incomplete dominance (a blend, e.g., pink flowers).

 

Question 5. In sickle cell co-dominant or incomplete dominance ?
Answer: Sickle cell anemia exhibits aspects of both incomplete dominance and codominance, depending on the level of observation:

• **At the organismal (phenotypic) level, it shows incomplete dominance:** Individuals heterozygous for the sickle cell allele (\(Hb^A Hb^S\)) have sickle cell trait. This is an intermediate condition, as they produce both normal and sickled red blood cells and are generally healthy, unlike those with full sickle cell anemia (\(Hb^S Hb^S\)).
• **At the molecular level, it shows codominance:** In heterozygotes, both normal hemoglobin (\(Hb^A\)) and sickle cell hemoglobin (\(Hb^S\)) proteins are produced. This equal expression of both types of hemoglobin molecules demonstrates codominance.

In simple words: Sickle cell shows incomplete dominance because people with one sickle cell gene have a "trait" that's in-between normal and full sickness. But at a tiny level, both types of blood cells are made, which is like codominance.

🎯 Exam Tip: Remember that sickle cell inheritance is a classic example that can illustrate both incomplete dominance (phenotype) and codominance (molecular expression) depending on the level of observation.

 

Question 6. Write a note on co-dominance ?
Answer: Codominance is a genetic relationship where both alleles for a trait are fully and equally expressed in a heterozygous individual. This means that instead of one allele masking the other (dominance) or blending to form an intermediate (incomplete dominance), both traits are distinctly visible. A classic example is the human ABO blood group, where if an individual inherits both A and B alleles, they express both, resulting in blood type AB. Each allele contributes to the phenotype without suppressing the other.
In simple words: Codominance means that if an organism gets two different genes for a trait, both genes show up fully at the same time, without mixing.

🎯 Exam Tip: Highlight that in codominance, "both alleles are fully and equally expressed," leading to both traits being visible.

 

Question 7. Across between Bbcc and Bbcc. What is the probability of Bbcc?
Answer: To find the probability of obtaining offspring with genotype Bbcc from a cross of Bbcc x Bbcc, we analyze each gene independently:

• **For the 'B' gene (Bb x Bb):**

  	B	b
  B	BB	Bb
  b	Bb	bb

  The probability of offspring being Bb is \( \frac{2}{4} = \frac{1}{2} \).
• **For the 'c' gene (cc x cc):**

  	c	c
  c	cc	cc
  c	cc	cc

  The probability of offspring being cc is \( \frac{4}{4} = 1 \).

To find the probability of Bbcc, we multiply the individual probabilities: \( P(\text{Bbcc}) = P(\text{Bb}) \times P(\text{cc}) = \frac{1}{2} \times 1 = \frac{1}{2} \).
In simple words: To find the chance of getting Bbcc from crossing Bbcc with Bbcc, we look at each gene separately. For the 'B' gene, there's a 1-in-2 chance of getting Bb. For the 'c' gene, there's a 100% chance of getting cc. So, the total chance is \( \frac{1}{2} \).

🎯 Exam Tip: When calculating probabilities for multiple genes, treat each gene's inheritance as an independent event and multiply their individual probabilities.

 

Question 8. Write a note on Homologous chromosome or homologous.
Answer: Homologous chromosomes are pairs of chromosomes that are similar in their morphological structure, physiological function, and genetic content. They are found in diploid cells, where one chromosome of the pair is inherited from the maternal parent and the other from the paternal parent. These chromosomes carry genes for the same traits at corresponding loci, although the alleles may be different. They are crucial for sexual reproduction as they pair up during meiosis. This ensures that each gamete receives one chromosome from each homologous pair, maintaining genetic consistency.
In simple words: Homologous chromosomes are matching pairs of chromosomes in a cell. One comes from the mother, and one from the father, and they carry genes for the same traits.

🎯 Exam Tip: Key features of homologous chromosomes are their "similar size and shape," "gene sequence," and origin from "each parent."

 

Question 9. Write a note Emasculation.
Answer: Emasculation is a plant breeding technique involving the removal of the anthers (male reproductive parts) from a flower. This process is carried out carefully before the anthers mature and release pollen. Its main purpose is to prevent self-pollination in bisexual flowers, ensuring that only desired pollen from another specific plant is used for cross-pollination. This controlled pollination helps in creating new hybrid varieties with desired characteristics.
In simple words: Emasculation is taking out the male part (anther) of a flower to stop it from pollinating itself. This lets scientists use pollen from a different flower instead.

🎯 Exam Tip: Remember that emasculation is done "before anthers mature" and its purpose is to "prevent self-pollination" for controlled cross-breeding.

 

Question 10. What is Punnett square or checker board?
Answer: A Punnett Square, also known as a checkerboard, is a graphical representation used in genetics to calculate the probability of all possible genotypes of offspring resulting from a genetic cross. It was developed by Reginald C. Punnett. This square diagram arranges the gametes of one parent along the top and the gametes of the other parent along the side, showing all potential allele combinations in the offspring. It helps in predicting genetic outcomes.
In simple words: A Punnett square is a chart used in genetics to show all the possible gene combinations and how likely they are when two parents have children.

🎯 Exam Tip: Emphasize that the Punnett square "calculates probabilities" and graphically represents "possible genotypes."

 

Question 11. Distinguish between homozygous and heterozygous
Answer:

• **Homozygous:**
  1. An organism is homozygous if it possesses identical alleles (e.g., TT or tt) for a specific trait.
  2. These individuals are considered pure-breeding or true-breeding lines.
  3. They produce only one type of gamete for the trait in question.
  4. Examples: Tall plants (TT) or dwarf plants (tt).
• **Heterozygous:**
  1. An organism is heterozygous if it possesses dissimilar alleles (e.g., Tt) for a specific trait.
  2. These individuals are referred to as hybrids.
  3. They produce more than one type of gamete (e.g., T and t) for that trait.
  4. Example: Tall plants (Tt).

In simple words: Homozygous means having two identical copies of a gene, like two "tall" genes. Heterozygous means having two different copies, like one "tall" and one "short" gene.

🎯 Exam Tip: For distinction, focus on "identical alleles" vs. "dissimilar alleles" and their impact on gamete production and breeding.

 

Question 12. Differentiate dominant from recessive character.
Answer:

In simple words: A dominant trait is one that always shows up, even if there's only one copy of its gene. A recessive trait only shows up if there are two copies of its gene.

🎯 Exam Tip: Remember the \(F_1\) generation rule: dominant traits appear, recessive ones are hidden. Also, note the genotype (homozygous vs. heterozygous) required for each to be expressed.

 

Question 13. Differentiate between Phenotype and Genotype
Answer:

• **Phenotype:**
  1. This refers to the observable physical appearance and characteristics of an organism.
  2. It can be directly seen or measured, such as tallness, eye color, or round seed shape.
  3. The phenotype is influenced by both the organism's genetic makeup (genotype) and environmental factors. For example, a plant with genotype Tt will have a Tall phenotype.
• **Genotype:**
  1. This refers to the genetic constitution or internal genetic makeup of an organism.
  2. It cannot be directly seen; it is the set of alleles an organism possesses (e.g., TT, Tt, tt).
  3. The genotype primarily determines the potential phenotype, but the actual expression can be modified by the environment. For example, a Tall phenotype could be due to either a TT or Tt genotype.

In simple words: Phenotype is what you see (like blue eyes), while genotype is the hidden genetic code that makes those blue eyes.

🎯 Exam Tip: The key difference is "observable characteristics" (phenotype) versus "genetic makeup" (genotype). Phenotype is influenced by both genes and environment.

 

Question 14. List out the several traits in pea selected by Mendel.
Answer: Mendel carefully chose seven different contrasting traits in pea plants for his experiments. These traits helped him understand how characteristics are passed down.

In simple words: Mendel looked at seven clear differences in pea plants, like tall or short stems, and used them to study how traits are passed on.

🎯 Exam Tip: When listing Mendel's traits, remember to mention both the dominant and recessive forms for each characteristic to score full marks.

 

Question 15. Draw the flow chart for heterozygous tall X homozygous dwarf pisum sativum plants If heterozygous tall test cross
Answer: This diagram shows a test cross where a heterozygous tall pea plant (Tt) is crossed with a homozygous dwarf pea plant (tt). This type of cross helps determine the genotype of the tall parent.

In simple words: When you cross a plant that is mixed (heterozygous tall) with one that is pure short (homozygous dwarf), you get half tall and half dwarf offspring. This helps you find out the genetic makeup of the parent.

🎯 Exam Tip: Always clearly label the parents, gametes, and F1 generation in a Punnett square to show the genetic outcomes correctly.

 

Question 16. Distinguish between monohybrid cross and dihybrid cross
Answer: Monohybrid and dihybrid crosses are different ways to study how traits are passed from parents to offspring, focusing on the number of traits at a time.

In simple words: A monohybrid cross looks at one trait, while a dihybrid cross looks at two traits at the same time.

🎯 Exam Tip: Clearly state the number of traits studied in each cross and their respective F2 phenotypic ratios for a complete answer.

 

Question 17. Distinguish between Test cross and Back cross
Answer: Test cross and back cross are two genetic crosses used to understand the genetic makeup of an organism, but they have distinct purposes.

In simple words: A test cross always uses a recessive parent to find the unknown genotype, while a back cross can use either parent to get specific traits.

🎯 Exam Tip: Highlight that a test cross specifically uses a recessive parent to reveal the genotype, while a back cross has a broader application for breeding purposes.

 

Question 18. What is genetic testing?
Answer: Genetic testing is a medical process that looks at your genes, chromosomes, or proteins to find changes that might indicate a genetic disorder, a risk of developing a disease, or to confirm a diagnosis. This can help predict if you might pass certain conditions to your children.
In simple words: Genetic testing checks your DNA for changes that could cause diseases or show your risk for certain health problems.

🎯 Exam Tip: Mentioning that genetic testing helps determine predisposition to health conditions or confirm diagnoses is key for a complete answer.

 

Question 19. What are genetic disorder?
Answer: Genetic disorders are health problems caused by changes or mutations in a person's genes or chromosomes. These changes can prevent proteins from working correctly, leading to various symptoms and conditions. For example, some genetic disorders affect how the body uses sugar.
In simple words: Genetic disorders happen when there are mistakes in our genes or chromosomes, which can stop our bodies from working properly.

🎯 Exam Tip: Define genetic disorders as conditions caused by gene or chromosome mutations, emphasizing that they often result in missing or inactive protein products.

 

Question 20. Write a short note on 'Mutation'?
Answer: A mutation is a sudden, inheritable change in the DNA sequence or chromosome structure. These changes can be caused by various agents called mutagens. Mutations can lead to new traits or abnormalities in future generations, some of which might be beneficial, and others harmful. For example, some mutations can lead to disease, while others can help an organism adapt to its environment.
In simple words: A mutation is a sudden change in an organism's DNA that can be passed down. These changes can be good or bad for the organism.

🎯 Exam Tip: Define mutation as a sudden, inheritable change in DNA/chromosomes, and mention both its causes (mutagens) and potential effects (new traits, abnormalities).

 

Question 21. Co-dominance is an example of intragenic gene interaction. How?
Answer: Co-dominance is an example of intragenic gene interaction because it involves two different alleles of the same gene that are both fully expressed in a heterozygous individual. Neither allele completely masks the other; instead, both traits appear simultaneously.

• The phenomenon where both alleles are expressed in the heterozygote is known as codominance.
• Examples include red and white flowers of camellia, where patches of both colors appear, and the inheritance of sickle cell hemoglobin.
• The ABO blood group system in humans also shows co-dominance, as both \( I^A \) and \( I^B \) alleles for the \( I \) gene are expressed equally when present together, resulting in AB blood type.

In simple words: Co-dominance happens when two different forms of the same gene both show up completely in an individual, like having both red and white patches on a flower, because neither gene is stronger than the other.

🎯 Exam Tip: For co-dominance, emphasize that both alleles are *fully and simultaneously expressed* in heterozygotes, using examples like ABO blood groups or flower colors.

 

Question 23. What is the different between sex linked and sex influenced diseases?
Answer: Sex-linked and sex-influenced diseases both relate to gender but differ in how their genes are carried. Sex-linked diseases are caused by genes found directly on the sex chromosomes (X or Y), meaning their inheritance patterns are often different for males and females. For example, color blindness is a sex-linked trait. In contrast, sex-influenced diseases are caused by genes located on non-sex chromosomes (autosomes), but their expression is affected by a person's sex hormones. This means a trait might be dominant in one sex and recessive in the other.
In simple words: Sex-linked diseases come from genes on X or Y chromosomes, making them appear more in one sex. Sex-influenced diseases are on other chromosomes, but hormones make them show up differently in males and females.

🎯 Exam Tip: Clearly state that sex-linked genes are on sex chromosomes, while sex-influenced genes are on autosomes but their expression is modified by sex hormones.

 

Question 24. What is Genome?
Answer: A genome is the complete set of all the genetic material (DNA or RNA) within an organism. It contains all the instructions needed for an organism to develop, function, and reproduce. Thinking of it as a complete instruction manual for life helps understand its significance.
In simple words: A genome is all the DNA an organism has, like a complete instruction book for its entire body and life.

🎯 Exam Tip: Emphasize that a genome is the *complete* set of genetic material (DNA/RNA) of an organism.

 

Question 25. What are lethal gene or lethal allele?
Answer: A lethal gene, or lethal allele, is a gene that can cause the death of an organism, often before birth or at a very early stage of development. These genes typically arise from mutations in genes that are vital for normal growth. Lethal alleles can be recessive (only causing death when two copies are present), dominant (causing death with just one copy), or conditional (causing death only under certain environmental conditions). For instance, a gene that causes a severe growth defect could be lethal.
In simple words: A lethal gene is a gene that causes an organism to die, usually very early in its life, because it changes something important for growth.

🎯 Exam Tip: Define lethal alleles as genes causing death, and mention they often result from mutations in essential developmental genes, specifying if they are dominant or recessive.

 

Question 26. What do you mean by inheritance of sickle cell anemia in man.
Answer: Sickle cell anemia is a genetic disease caused by a specific gene (Hbs) that affects hemoglobin, the protein in red blood cells that carries oxygen. If a person inherits two copies of this gene (homozygous, Hbs/Hbs), they develop severe anemia and often die. However, if they inherit one copy of the Hbs gene and one normal gene (heterozygous, HbA/Hbs), they have sickle cell trait. This trait gives them some protection against malaria and usually causes milder or no symptoms, showing incomplete dominance.
In simple words: Sickle cell anemia is a blood disease caused by a gene that changes red blood cells. Having two copies of this gene is very serious, but having one copy gives a milder trait and even protection against malaria.

🎯 Exam Tip: Explain that sickle cell anemia is lethal in homozygous individuals (Hbs/Hbs) but presents as a milder, protective sickle cell trait in heterozygous carriers (HbA/Hbs).

 

Question 27. What is cytoplasmic male sterility?
Answer: Cytoplasmic male sterility (CMS) is a condition in plants where they cannot produce functional pollen grains, making them unable to fertilize. This trait is not inherited through Mendel's rules but is passed down maternally, meaning it comes only from the female parent. This happens because the genes responsible for CMS are found in the mitochondria, which are inherited from the egg cell. The presence of these mitochondrial genes affects the plant's ability to produce fertile pollen.

• Plants that cannot produce functional pollen grains are called male-sterile.
• If this sterility is passed down from the mother plant and not through Mendelian rules, it is known as cytoplasmic male sterility (CMS).
• The genes for cytoplasmic male sterility are located in the mitochondrial DNA.

In simple words: Cytoplasmic male sterility means a plant cannot make good pollen, and this trait is inherited only from the mother plant, usually due to genes in the mitochondria.

🎯 Exam Tip: Highlight that cytoplasmic male sterility is maternally inherited (non-Mendelian) and caused by genes in mitochondrial DNA, leading to non-functional pollen.

 

Question 28. Briefly explain 'Atavism' with suitable examples.
Answer: Atavism is when an ancestral trait, which was lost through evolution, reappears in an organism. The word "atavism" comes from the Latin word "atavius," meaning "ancestor." This is a modification of a biological structure, and it shows traits from a distant past relative, not just immediate parents. For example, the re-emergence of sexual reproduction in the flowering plant *Hieracium pilosella* is considered a good example of atavism.
In simple words: Atavism is when an old trait from a distant ancestor shows up again in an animal or plant, even after it had disappeared for many generations.

🎯 Exam Tip: Define atavism as the reappearance of an ancestral trait that was previously lost, and provide a clear example like the sexual reproduction in *Hieracium pilosella*.

 

Question 29. How to do test for homozygosity of a trait in plant.
Answer: To find out if a plant showing a dominant trait is homozygous (pure) or heterozygous (mixed), a scientist can perform a test cross. In this method, the plant with the unknown genotype is crossed with a plant that is homozygous for the recessive trait.

• To identify whether an organism exhibiting a dominant trait is homozygous or heterozygous for a specific allele, a scientist performs a test cross.
• The organism with the dominant trait is crossed with an organism that is homozygous for the recessive trait.
• By observing the offspring of this test cross, one can determine the genotype of the unknown parent. If all offspring show the dominant trait, the parent was homozygous dominant. If some offspring show the recessive trait, the parent was heterozygous.

In simple words: To check if a plant with a strong trait is pure or mixed, you cross it with a plant that has the weak trait. How the babies look will tell you if the first plant was pure.

🎯 Exam Tip: Emphasize that a test cross involves crossing an individual with an unknown dominant genotype with a homozygous recessive individual, and the offspring phenotypes reveal the unknown genotype.

 

Question 1. Difference between Pleiotropy and polygenic inheritance with suitable examples.
Answer: Pleiotropy and polygenic inheritance are both genetic phenomena, but they describe different ways genes influence traits. Pleiotropy is when one single gene affects multiple different traits or characteristics. For example, Marfan syndrome, a human genetic disorder, is caused by a single gene mutation but affects height, fingers, toes, lens dislocation, and heart function. This shows one gene having many effects.
In contrast, polygenic inheritance is when one single trait is controlled by multiple genes working together. For instance, human skin color or height is determined by several genes, not just one. Each gene adds a small amount to the final trait, resulting in a continuous range of variation.
In simple words: Pleiotropy is when one gene controls many different things about you, like how a single gene might affect your height and eye color. Polygenic inheritance is when many different genes work together to control just one thing, like how many genes make up your skin color.

🎯 Exam Tip: Clearly differentiate between "one gene, many effects" (pleiotropy) and "many genes, one effect" (polygenic inheritance), providing a specific example for each.

 

Question 2. Co-dominance and incomplete dominance are not the same? why?
Answer: Co-dominance and incomplete dominance are not the same because they result in different ways alleles are expressed in a heterozygote.

• In co-dominance, neither allele is dominant over the other. Instead, both alleles are fully and equally expressed at the same time in the heterozygote. For example, in ABO blood groups, an individual with both A and B alleles expresses both types of antigens, resulting in AB blood type. There is no blending; both traits are distinctly visible.
• In incomplete dominance, neither allele is fully dominant, leading to a blending of traits in the heterozygote. The resulting phenotype is an intermediate mix of the two parent phenotypes. For example, if a red flower (RR) is crossed with a white flower (WW), the offspring (RW) will be pink. The red and white colors literally blend to make a new color.

In simple words: Co-dominance shows both traits fully at the same time, like polka dots. Incomplete dominance creates a new, mixed trait, like making pink from red and white.

🎯 Exam Tip: Emphasize "simultaneous, distinct expression" for co-dominance versus "blending or intermediate phenotype" for incomplete dominance.

 

Question 3. Difference between Monohybrid cross and Reciprocal cross.
Answer: Monohybrid and reciprocal crosses are both used in genetics, but they focus on different aspects of inheritance.

In simple words: A monohybrid cross just tracks one trait, but a reciprocal cross swaps which parent is male or female to see if the trait is linked to sex or comes from the cell's cytoplasm.

🎯 Exam Tip: For reciprocal crosses, remember its main purpose is to test for the influence of sex-linked or cytoplasmic inheritance by reversing the parent's sex roles.

 

Question 4. Difference between Monohybrid and Dihybrid cross
Answer: Monohybrid and dihybrid crosses are fundamental tools in genetics, differing in the number of traits they investigate simultaneously.

In simple words: A monohybrid cross tracks one trait from parents to offspring, while a dihybrid cross tracks two traits at the same time to see how they combine.

🎯 Exam Tip: When comparing, always include the number of traits examined and the resulting F2 phenotypic ratios for both crosses.

 

Question 5. Explain Monohybird cross.
Answer: A monohybrid cross is a genetic cross between two individuals that focuses on the inheritance pattern of a single contrasting trait. This cross helps to understand how one specific characteristic is passed from parents to offspring. For example, if we cross a pure tall pea plant with a pure dwarf pea plant, the F1 generation will all be tall. When the F1 generation self-pollinates, the F2 generation will show a 3:1 phenotypic ratio (3 tall to 1 dwarf) and a 1:2:1 genotypic ratio. This experiment demonstrates Mendel's Law of Segregation.

In simple words: A monohybrid cross tracks one trait, like flower color, from one generation to the next. It helps us see how dominant and recessive versions of a gene show up in the offspring.

🎯 Exam Tip: When explaining a monohybrid cross, clearly define it as studying one trait and include the expected F2 phenotypic (3:1) and genotypic (1:2:1) ratios.

 

Question 6. Explain Dihybrid cross.
Answer: A dihybrid cross is a genetic cross between two individuals that focuses on the inheritance of two different contrasting traits simultaneously. This helps to understand how two different characteristics are passed down and assort independently of each other. For example, Mendel crossed pea plants with round yellow seeds (RRYY) with plants having wrinkled green seeds (rryy). The F1 generation all had round yellow seeds (RrYy). When these F1 plants self-pollinated, the F2 generation showed a phenotypic ratio of 9:3:3:1, demonstrating the Law of Independent Assortment.

In simple words: A dihybrid cross looks at two different traits at the same time, like seed shape and color, to see how they are passed on together and if they affect each other.

🎯 Exam Tip: Remember that a dihybrid cross always demonstrates Mendel's Law of Independent Assortment with a characteristic 9:3:3:1 phenotypic ratio in the F2 generation.

 

Question 7. Briefly explain Trihybrid cross.
Answer: A trihybrid cross is a genetic experiment where two individuals that are homozygous for three different traits are crossed. For example, crossing a pure tall, yellow, round pea plant (TTYYRR) with a pure dwarf, green, wrinkled pea plant (ttyyRR). The F1 generation will be heterozygous for all three traits (TtYyRr). When these F1 individuals are self-pollinated, the F2 generation will show a complex phenotypic ratio of 27:9:9:9:3:3:3:1. This cross helps to understand the independent assortment of three distinct gene pairs.

In simple words: A trihybrid cross involves tracking three different traits at once to see how they all get passed down and mixed in new generations.

🎯 Exam Tip: When describing a trihybrid cross, state that it involves three traits and recall the characteristic F2 phenotypic ratio of 27:9:9:9:3:3:3:1.

 

Question 8. What traits are determined by multiple alleles?
Answer: Multiple alleles refer to situations where a single gene has more than two possible alleles (forms) in a population, rather than the usual two. While an individual can only carry two alleles, many more can exist within the overall population. These multiple alleles interact to determine a trait, often leading to more than just two phenotypes.

• Blood type is a common example of a multiple allele trait. There are three different alleles for human blood type: \( I^A \), \( I^B \), and \( i \).
• \( I^A \) and \( I^B \) are dominant over \( i \), and they are co-dominant with each other. This means they both fully express when present together.
• These alleles combine to produce four main blood phenotypes: A, B, AB, and O. For example, a person with an \( I^A \) allele and an \( i \) allele will have blood type A.

In simple words: Multiple alleles mean there are more than two choices for a single gene in a group of organisms, like how human blood types (A, B, AB, O) come from three different gene options.

🎯 Exam Tip: When discussing multiple alleles, define it as more than two alleles for a single gene in a population and use the human ABO blood group system as the primary example, explaining its dominance and co-dominance patterns.

 

Question 9. What is a gene?
Answer: A gene is a basic unit of heredity, made up of a sequence of DNA or RNA. It carries the instructions for making a specific protein or RNA molecule, which in turn determines a particular trait or characteristic in an organism. Genes are passed from parents to offspring and are essential for controlling all biological processes. For example, a gene might carry the instruction for eye color.
In simple words: A gene is a tiny instruction on our DNA that tells our body how to make something specific, like eye color, and it gets passed down from our parents.

🎯 Exam Tip: Define a gene as the basic unit of heredity, emphasizing its role in carrying instructions for a specific trait or protein.

 

Question 10. What is Incomplete dominance with example.
Answer: Incomplete dominance is a genetic situation where one allele does not completely dominate another. This leads to a new, intermediate phenotype that is a mix of both parent traits. For example, if you cross a pure red flower (R¹R¹) with a pure white flower (R²R²), the first generation (F₁) will have pink flowers (R¹R²). When these F₁ pink flowers are self-pollinated, the F₂ generation will show a phenotypic ratio of 1 red : 2 pink : 1 white, and a genotypic ratio of 1 R¹R¹ : 2 R¹R² : 1 R²R². This shows that the original traits reappear, confirming the particulate nature of inheritance.
In simple words: When two different genes meet, instead of one fully winning, they mix to make a new, in-between trait. Like mixing red and white paint to get pink.

🎯 Exam Tip: Remember that incomplete dominance leads to a blended phenotype, so the heterozygous individual will look different from both homozygous parents.

 

Question 11. Briefly explain about lethal gene.
Answer: Lethal alleles, also known as lethal genes, are specific versions of a gene that can cause an organism to die when present. These genes usually come from mutations in genes that are very important for normal growth or development. Lethal genes can lead to death before birth, after birth, or at any stage of life, depending on the gene. They can be recessive, dominant, or even conditional, meaning they only cause death under certain conditions or when combined with other specific genes.
In simple words: A lethal gene is a faulty gene that can cause an organism to die. It often affects important body functions.

🎯 Exam Tip: When explaining lethal genes, it's key to mention their origin (mutation) and their impact (death at various developmental stages).

 

Question 12. Explain epistatsis and its two types.
Answer: Epistasis is a gene interaction where one gene influences the expression of another gene, which is not an allele of the first. The gene that hides or masks the effect of another gene is called the epistatic gene, while the gene whose expression is suppressed is called the hypostatic gene. This interaction is different from simple dominance where alleles of the same gene interact. A common example is coat color in mice, where a gene for albinism can hide the expression of genes for other colors.
There are two main types:
1. Dominant Epistasis: This happens when a dominant allele of one gene masks the expression of all alleles (both dominant and recessive) of another gene. For example, in summer squash, a dominant gene for white color (W) masks the expression of genes for yellow (Y) or green (y) fruit color.
2. Recessive Epistasis: This happens when a recessive allele (in homozygous form) of one gene masks the phenotypic expression of the dominant allele of another gene. For instance, in mice, the 'c' allele (recessive) for albinism, when homozygous (cc), prevents the expression of the gene for coat color (A/a), resulting in an albino mouse even if a dominant color gene is present.
In simple words: Epistasis is when one gene acts like a boss and stops another gene from showing its trait. Dominant epistasis happens if the "boss" gene is dominant, and recessive epistasis happens if the "boss" gene is recessive.

🎯 Exam Tip: To differentiate between dominant and recessive epistasis, identify which gene (and which allele of that gene) is responsible for masking the other gene's effect.

 

Question 13. Describe dominant epistasis with an example.
Answer: If two genes have homozygous recessive alleles, and both produce the same visible characteristic (phenotype), their interaction is known as complementary gene interaction. This means that both dominant alleles need to be present to show a certain trait. The F₂ ratio in this case is 9:7, instead of the expected 9:3:3:1 for a dihybrid cross. For example, in sweet peas (Lathyrus odoratus), Bateson and Punnett crossed two varieties of white flowers (CCpp x ccPP). Both parents have white flowers because they each lack one of the dominant genes needed to produce the purple pigment. However, when these are crossed, the F₁ generation produces purple flowers (CcPp), because they now have both dominant alleles (C and P) required to produce the pigment. When these F₁ plants are self-crossed, the F₂ generation shows a 9:7 ratio of purple to white flowers, as only individuals with at least one dominant C and one dominant P allele will be purple.
In simple words: Complementary genes work together, like two puzzle pieces. If you don't have both dominant pieces, the trait won't show up.

🎯 Exam Tip: Remember that complementary genes require at least one dominant allele from EACH gene pair to express the trait. The 9:7 ratio is a key indicator.

 

Question 14. Explain duplicate gene with cumulative effect (9:6:1)
Answer: Duplicate genes with cumulative effect mean that two different genes can produce the same trait, and their effects add up. If both dominant alleles are present, they contribute to the trait, and the more dominant alleles you have, the stronger the trait. For example, in fruit shape of summer squash, there are two gene pairs that affect shape. If both dominant alleles (A and B) are present together, they result in a disc-shaped fruit. If only one dominant allele (A or B) is present, the fruit is sphere-shaped. If neither dominant allele is present (aabb), the fruit is long-shaped. This produces an F₂ phenotypic ratio of 9:6:1 (9 disc, 6 sphere, 1 long). This shows that different genes can work together to create a range of phenotypes.
In simple words: When two genes do the same job, their powers add up. More "strong" genes mean a stronger trait, like getting different fruit shapes depending on how many strong genes are there.

🎯 Exam Tip: For duplicate genes, remember the 9:6:1 ratio for fruit shape in squash. This pattern shows how multiple genes can contribute to a trait with an additive effect.

 

Question 15. What are Duplicate dominant gene (15:1) or duplicate gene?
Answer: Duplicate dominant genes are when two different dominant genes can produce the same specific phenotype, without any combined or additive effect. If either dominant gene is present, the trait will appear. Only when both genes are in their homozygous recessive form will a different phenotype be expressed. This results in an F₂ phenotypic ratio of 15:1. A classic example is the seed capsule shape in shepherd's purse. The triangular shape is dominant, and if a dominant allele from either of two gene pairs (A or B) is present, the capsule will be triangular. Only if both genes are recessive (aabb) will the capsule be ovoid (top-shaped). This means that 15 out of 16 offspring will have the triangular shape, and only 1 will have the ovoid shape.
In simple words: If you have two different strong genes, and either one can create the same trait by itself, then almost all offspring will show that trait. Only if both genes are "weak" will another trait appear.

🎯 Exam Tip: The 15:1 ratio for duplicate dominant genes is a clear sign that either dominant allele can produce the trait, and only the complete absence of dominant alleles (double recessive) results in the alternative phenotype.

 

Question 16. Explain dominant and recessive interaction (or) inhibitor gene (13:3)
Answer: Dominant and recessive interaction, also known as inhibitor gene interaction, occurs when the dominant allele of one gene (say, A) can prevent the expression of another gene (B) in its homozygous and heterozygous forms (AA, Aa). Additionally, the homozygous recessive alleles (bb) of a third gene can also mask the expression. This leads to an F₂ phenotypic ratio of 13:3. An example is feather color in fowl. A dominant allele for inhibition (I) prevents any color from appearing, making the fowl white. If the inhibitor gene is recessive (ii), then a color gene (C) can be expressed, leading to colored fowl. So, a dominant inhibitor gene (I) masks all color genes, while the recessive inhibitor gene (ii) allows color to show. This means that a wide range of genotypes will result in white feathers, while only a few specific genotypes will result in colored feathers.
In simple words: One gene can "turn off" another gene's effect, making it seem like a trait is missing. If the "off" switch is dominant, it often results in a very high number of offspring without that trait.

🎯 Exam Tip: When dealing with inhibitor genes, identify which genotype combinations lead to the masked phenotype (e.g., white) and which allow the actual trait (e.g., colored) to be expressed.

 

Question 17. Male sterility found in pearl maize (sorgum Vulgare) is the best example for mitochondria cytoplasmic inheritance.
Answer: Male sterility in pearl maize (Sorghum vulgare) is an excellent example of mitochondrial cytoplasmic inheritance. This means that the trait for male sterility is passed down through the cytoplasm of the egg cell from the mother, not through the nucleus or pollen from the father. In these plants, male sterility is inherited maternally, so only the female parent's genetic information in the cytoplasm (specifically from the mitochondria) determines if the offspring will be male sterile. This is a crucial concept in plant breeding for developing hybrid varieties, as it controls pollen production, a key part of reproduction.
In simple words: In some plants like pearl maize, if the mother plant is male-sterile, all her offspring will also be male-sterile. This is because the genes for sterility are in the mitochondria, which are passed down only from the mother.

🎯 Exam Tip: Cytoplasmic inheritance is always maternal, meaning traits are passed from the mother, and involves genes found outside the nucleus, like in mitochondria or chloroplasts.

 

Question 18. What is genetic testing?
Answer: Genetic testing is a medical process that examines an individual's DNA to identify changes in chromosomes, genes, or proteins. It can be used for various reasons, such as confirming a diagnosis of a genetic disease, identifying a predisposition to a certain health condition, or determining if someone is a carrier for a genetic disorder that could be passed to their children. These tests provide valuable information for personalized medicine and family planning.
In simple words: Genetic testing looks at your DNA to find differences that might cause diseases or be passed to your children. It helps doctors understand your health better.

🎯 Exam Tip: When defining genetic testing, include its purpose (diagnosis, risk assessment, carrier status) and the biological basis (DNA analysis).

 

Question 19. What are genetic disorder ?
Answer: Genetic disorders are health problems caused by changes or errors in an individual's genes or chromosomes. These changes can prevent genes from working correctly, leading to the production of faulty or missing proteins. Genetic disorders are often characterized by the absence of or inactive protein products. They can be inherited from parents or occur spontaneously due to new mutations, causing a wide range of physical and developmental issues.
In simple words: Genetic disorders happen when there's a mistake in a person's genes or chromosomes, which can make their body not work correctly.

🎯 Exam Tip: Focus on gene malfunctions and their impact on protein production as the core of genetic disorders.

 

Question 20. Write a short note on 'Mutation'?
Answer: A mutation is a sudden, inheritable change in the DNA sequence or chromosome structure of an organism. These changes can be caused by various agents called mutagens, such as radiation or certain chemicals. Mutations can be small, like a single base change in DNA, or large, like changes in whole chromosomes. While some mutations can be harmful, leading to abnormalities or diseases, others can be beneficial or neutral, providing the raw material for evolution by introducing new genetic variations into a population.
In simple words: A mutation is a sudden change in a gene or chromosome. It can be good, bad, or make no difference, and can be passed to offspring.

🎯 Exam Tip: Emphasize that mutations are inheritable changes in DNA/chromosomes and can be caused by mutagens, leading to varying effects on an organism.

 

Question 21. Co-dominance is an example of intragenic gene interaction. How?
Answer: Co-dominance is an example of intragenic gene interaction because both alleles of a single gene are expressed equally and simultaneously in the heterozygous individual. Unlike incomplete dominance, where a blend occurs, in co-dominance, both traits are distinctly visible. For instance, in ABO blood group system in humans, the I^A and I^B alleles are co-dominant. If a person inherits both I^A and I^B alleles, they will have blood type AB, meaning both A and B antigens are present on their red blood cells. Another example is the red and white flowers of camellia, where a heterozygous plant displays both red and white petals, showing both traits clearly, not a mixed pink color.
In simple words: Co-dominance is when both versions of a gene show up fully at the same time in an individual, like having both A and B blood types.

🎯 Exam Tip: For co-dominance, remember that *both* alleles are expressed, leading to distinct traits appearing together, not a blended intermediate.

 

Question 23. What is the different between sex linked and sex influenced diseases ?
Answer: Sex-linked diseases are caused by genes located on the sex chromosomes, primarily the X chromosome. These diseases, like color blindness or hemophilia, are often expressed differently in males and females because males only have one X chromosome (XY) while females have two (XX). Sex-influenced diseases, on the other hand, are caused by genes located on autosomal chromosomes (non-sex chromosomes), but their expression is affected by an individual's sex hormones. This means a trait might be dominant in one sex and recessive in the other, even though the genes are not on sex chromosomes. For example, male-pattern baldness is influenced by sex hormones, appearing more frequently and severely in males.
In simple words: Sex-linked diseases are on the X or Y chromosome, affecting males and females differently. Sex-influenced diseases are on regular chromosomes, but hormones make them show up more in one sex than the other.

🎯 Exam Tip: The key difference is the location of the gene: sex-linked are on sex chromosomes, while sex-influenced are on autosomes but affected by hormones.

 

Question 24. What is Genome ?
Answer: A genome is the complete set of genetic instructions present in an organism. It includes all of its DNA (or RNA in some viruses), encompassing all genes, non-coding regions, and mitochondrial or chloroplast DNA. The genome carries all the information needed to build and maintain an organism, and it is passed down from one generation to the next. Understanding an organism's genome is crucial for studying its development, diseases, and evolutionary history.
In simple words: A genome is the entire book of instructions that tells a living thing how to grow and work, all written in its DNA.

🎯 Exam Tip: Define genome as the *complete* set of genetic material, emphasizing that it includes all DNA/RNA and instructions for an organism.

 

Question 25. What are lethal gene or lethal allele ?
Answer: Lethal alleles are gene variations that can cause the death of an organism, usually before it can reproduce. These alleles often arise from mutations in genes essential for normal development or survival. They can be dominant (where one copy is enough to cause death), recessive (where two copies are needed), or conditional (where death occurs only under specific environmental conditions). Organisms carrying lethal alleles might die at any stage, from embryo to adulthood, depending on the gene and its expression timing. For instance, the 'yellow' coat color gene in mice is lethal in its homozygous dominant form, leading to embryonic death.
In simple words: Lethal genes are faulty genes that can kill a living thing. They come in different types, but all stop an organism from living.

🎯 Exam Tip: Clearly state that lethal alleles cause death, often due to essential gene mutations, and can be dominant, recessive, or conditional.

 

Question 26. What do you mean by inheritance of sickle cell anemia in man.
Answer: Sickle cell anemia is a genetic blood disorder caused by a specific gene (Hb^S) that affects the shape of red blood cells. This disease shows a pattern of co-dominance and incomplete dominance. In individuals who are homozygous for the Hb^S gene (Hb^SHb^S), the red blood cells become sickle-shaped, leading to severe anemia, blockages in blood flow, and often early death; this is the lethal effect. However, individuals who are heterozygous (Hb^AHb^S) carry the sickle cell trait. They usually do not have severe symptoms but have some sickle-shaped cells and are resistant to malaria. This resistance is an example of heterozygote advantage, where carrying one copy of the gene provides a benefit, especially in malaria-prone regions.
In simple words: Sickle cell anemia is a blood problem caused by a special gene. If you have two copies of the gene, you get very sick. If you have one copy, you are usually healthy and even get protection from malaria.

🎯 Exam Tip: Explain both homozygous (severe anemia) and heterozygous (sickle cell trait, malaria resistance) conditions to fully describe sickle cell anemia inheritance.

 

Question 27. What is cytoplasmic male sterility ?
Answer: Cytoplasmic male sterility (CMS) is a condition in plants where they are unable to produce functional pollen, making them male-sterile. This trait is inherited maternally, meaning it is passed down from the mother plant through the cytoplasm of the egg cell, not through the nucleus or pollen. The genes responsible for CMS are typically found in the mitochondria, which are organelles in the cytoplasm. Since pollen only contributes nuclear DNA and not cytoplasm, male sterility is only inherited from the female parent. This phenomenon is very important in plant breeding, especially for producing hybrid seeds efficiently, as it prevents self-pollination and ensures cross-pollination. An example is the male sterility found in pearl maize.
In simple words: Cytoplasmic male sterility means a plant cannot make good pollen, and this trait is inherited only from the mother plant because the genes are in the cell's cytoplasm, not its main nucleus.

🎯 Exam Tip: Emphasize maternal inheritance and the role of mitochondrial genes in defining cytoplasmic male sterility.

 

Question 28. Briefly explain 'Atavism' with suitable examples.
Answer: Atavism refers to the reappearance of a trait in an organism after it has been lost for several generations, or when an organism shows a characteristic of a more distant ancestor rather than its immediate parents. This phenomenon is rooted in evolutionary biology and happens when ancestral genes, which were previously switched off, become active again due to specific genetic or developmental pathways. It's like a genetic "throwback" to an earlier evolutionary stage. A good example is the re-emergence of sexual reproduction in the flowering plant Hieracium pilosella, where some individuals can revert to sexual reproduction after generations of asexual reproduction. Another example is the occasional birth of a human with a tail-like appendage, which harks back to our mammalian ancestors.
In simple words: Atavism is when an animal or plant shows a trait from a very old ancestor that its recent parents didn't have. It's like a trait from the past coming back.

🎯 Exam Tip: When explaining atavism, highlight it as the re-emergence of an ancestral trait that was previously lost, giving examples like the Hieracium plant or human tail-like structures.

 

Question 29. How to do test for homozygosity of a trait in plant.
Answer: To determine if a plant showing a dominant trait is homozygous (pure breeding) or heterozygous (hybrid), a scientist can perform a test cross. In this process, the plant with the unknown genotype is crossed with a plant that is homozygous recessive for the same trait. The offspring of this test cross will reveal the genotype of the unknown parent. If all the offspring show the dominant trait, then the unknown parent was homozygous dominant. However, if some of the offspring show the recessive trait, then the unknown parent must have been heterozygous. This method is fundamental in genetics for identifying pure lines.
In simple words: To check if a plant is "pure" for a trait, you cross it with a "recessive" plant. If all babies look like the "pure" parent, it was pure. If some babies show the other trait, it was mixed.

🎯 Exam Tip: The key to a test cross is always crossing the unknown dominant phenotype with a homozygous recessive individual, then observing the F₁ generation.

 

Question 1. Difference between Pleiotropy and polygenic inheritance with suitable examples.
Answer:
Pleiotropy: This occurs when a single gene affects multiple distinct phenotypic traits. The gene has multiple effects, even though it's just one gene. For example, Marfan syndrome in humans is caused by a mutation in a single gene, but it affects connective tissue throughout the body, leading to symptoms like unusual tall height, long fingers and toes, dislocation of the eye lens, and heart problems. This illustrates how one gene can have a widespread impact.
Polygenic Inheritance: This occurs when one phenotypic trait is controlled by multiple genes, and their effects are often cumulative. Instead of one gene influencing many traits, many genes influence one trait. For example, human skin color and height are polygenic traits. Many different genes contribute to the amount of melanin (pigment) in the skin, resulting in a continuous range of skin tones rather than just a few distinct categories. This shows how multiple genes can work together to create a continuous variation in a trait.
In simple words: Pleiotropy is when one gene controls many different traits. Polygenic inheritance is when many different genes work together to control just one trait.

🎯 Exam Tip: Remember: "Pleo" means "many" (one gene, many traits) and "Poly" means "many" (many genes, one trait). Keep these distinct examples clear in your mind.

 

Question 2. Co-dominance and incomplete dominance are not the same? why?
Answer: Co-dominance and incomplete dominance are distinct forms of gene interaction, although both involve heterozygotes expressing characteristics different from homozygous parents. They are not the same because of how the alleles are expressed:
1. Incomplete Dominance: In this case, neither allele is completely dominant over the other. The heterozygous phenotype is an intermediate blend of the two homozygous phenotypes. For example, if a red flower is crossed with a white flower, the offspring might be pink. The red and white traits are blended to form a new, intermediate color.
2. Co-dominance: In this case, both alleles are fully expressed in the heterozygote without blending. Both traits appear distinctly and simultaneously. For example, in human ABO blood types, if an individual inherits both A and B alleles, they will have AB blood type, meaning both A and B antigens are present on their red blood cells. The traits are co-expressed, not mixed. Another example is roan cattle, where both red and white hairs are present, not a uniform pink color.
In simple words: They are different because incomplete dominance makes a mixed-up new trait (like pink from red and white), but co-dominance shows both traits fully at the same time (like red and white spots).

🎯 Exam Tip: The key distinction lies in blending versus simultaneous, distinct expression. Incomplete dominance is a blend, co-dominance is both visible.

 

Question 3. Difference between Monohybrid cross and Reciprocal cross.
Answer:
Monohybrid Cross:
1. A monohybrid cross involves mating two parents that differ in a single pair of contrasting characteristics. For example, crossing a tall pea plant with a dwarf pea plant to study the inheritance of height.
2. It primarily focuses on observing the inheritance pattern of one specific trait through generations.
3. The results help to understand the principles of dominance and segregation.
4. It does not typically reveal information about cytoplasmic inheritance or sex-linked traits because the parents' roles are fixed (e.g., a specific male and female).
Reciprocal Cross:
1. A reciprocal cross involves performing two crosses where the source of the gametes is reversed in the second cross. For example, if in the first cross, a tall female is mated with a dwarf male, in the reciprocal cross, a dwarf female is mated with a tall male.
2. It is used to determine if a trait is linked to the sex of the parent (sex-linked inheritance) or if it is determined by genes in the cytoplasm (maternal inheritance).
3. If the results of the two reciprocal crosses are the same, the trait is likely autosomal and not maternally inherited. If the results differ, it suggests sex-linkage or cytoplasmic inheritance.
4. It is essential for understanding more complex inheritance patterns beyond simple Mendelian traits.
In simple words: A monohybrid cross looks at how one trait is passed down. A reciprocal cross swaps the mother and father to see if the trait comes from the mother, father, or cytoplasm.

🎯 Exam Tip: Remember that a monohybrid cross studies one trait, while a reciprocal cross tests for sex-linkage or maternal inheritance by reversing the parent's sex for the traits being studied.

 

Question 4. Difference between Monohybrid and Dihybrid cross
Answer:
Monohybrid Cross:
1. A monohybrid cross studies the inheritance of a single pair of contrasting traits between two individuals. For instance, crossing a plant with tall stems and one with short stems.
2. The F₂ generation typically produces a phenotypic ratio of 3:1 (e.g., 3 tall to 1 dwarf).
3. The F₂ genotypic ratio is usually 1:2:1 (e.g., 1 TT : 2 Tt : 1 tt).
4. It is used to demonstrate Mendel's Law of Segregation, which states that alleles for each trait separate during gamete formation.
5. Only one pair of contrasting characteristics is involved.
Dihybrid Cross:
1. A dihybrid cross studies the inheritance of two pairs of contrasting traits simultaneously. For example, crossing a plant with round, yellow seeds with one that has wrinkled, green seeds.
2. The F₂ generation typically produces a phenotypic ratio of 9:3:3:1.
3. The F₂ genotypic ratio is 1:2:1:2:4:2:1:2:1.
4. It is used to demonstrate Mendel's Law of Independent Assortment, which states that alleles for different traits segregate independently of each other during gamete formation.
5. Two pairs of contrasting characteristics are involved.
In simple words: A monohybrid cross looks at one trait. A dihybrid cross looks at two traits at the same time to see how they are passed down together or separately.

🎯 Exam Tip: The key difference is the number of traits studied: one for monohybrid, two for dihybrid. Remember their respective F₂ phenotypic ratios: 3:1 for monohybrid and 9:3:3:1 for dihybrid.

 

Question 5. Explain Monohybird cross.
Answer: A monohybrid cross is a genetic cross between two individuals that focuses on the inheritance pattern of a single contrasting trait. It typically starts with crossing two pure-breeding parents (homozygous) that differ in one specific characteristic, such as pea plants with yellow seeds (YY) and green seeds (yy). The first filial (F₁) generation will all show the dominant trait (e.g., all yellow seeds, Yy). When these F₁ individuals are self-pollinated or crossed with each other, the second filial (F₂) generation will exhibit both the dominant and recessive traits in a predictable phenotypic ratio of 3:1 (e.g., 3 yellow to 1 green) and a genotypic ratio of 1:2:1 (1 YY : 2 Yy : 1 yy). This cross helps illustrate Mendel's Law of Segregation, which explains how alleles separate during gamete formation.
In simple words: A monohybrid cross studies how one single trait, like seed color, is passed from parents to offspring, showing how dominant and recessive traits appear in later generations.

🎯 Exam Tip: When drawing a Punnett square for a monohybrid cross, ensure all possible gamete combinations are shown, and correctly tally the genotypic and phenotypic ratios.

 

Question 6. Explain Dihybrid cross.
Answer: A dihybrid cross is a genetic experiment where two individuals are crossed to study the inheritance patterns of two different traits simultaneously. For example, Mendel crossed pea plants that differed in two traits: seed shape (round or wrinkled) and seed color (yellow or green). When pure-breeding round, yellow-seeded plants (RRYY) are crossed with pure-breeding wrinkled, green-seeded plants (rryy), the first filial (F₁) generation consists of all heterozygous round, yellow-seeded plants (RrYy). When these F₁ plants are self-pollinated or intercrossed, the second filial (F₂) generation produces a characteristic phenotypic ratio of 9:3:3:1. This ratio indicates 9 individuals with both dominant traits (round, yellow), 3 with one dominant and one recessive trait (round, green), 3 with the other dominant and recessive trait (wrinkled, yellow), and 1 with both recessive traits (wrinkled, green). This cross demonstrates Mendel's Law of Independent Assortment, showing that alleles for different traits are inherited independently of each other.
In simple words: A dihybrid cross is when we study how two different traits, like seed shape and color, are passed down at the same time. It shows if these traits are inherited together or separately.

🎯 Exam Tip: When solving dihybrid cross problems, accurately determine all possible gametes from each parent and construct a Punnett square to systematically predict F₂ genotypes and phenotypes.

 

Question 7. Briefly explain Trihybrid cross.
Answer: A trihybrid cross is a complex genetic cross that involves two individuals differing in three pairs of contrasting traits. For instance, crossing a tall, yellow, round-seeded pea plant (TTYYRR) with a dwarf, green, wrinkled-seeded plant (ttyyzz). The F₁ generation will consist of all heterozygous individuals (TtYyRr) showing all three dominant traits. When these F₁ individuals are self-pollinated, the F₂ generation will produce 8 different gametes and 64 different zygote combinations, leading to a phenotypic ratio of 27:9:9:9:3:3:3:1. This intricate cross demonstrates that the inheritance of each of the three traits is independent of the others, following Mendel's laws of segregation and independent assortment. It highlights how genetic variation increases with more traits involved in a cross.
In simple words: A trihybrid cross studies three different traits at the same time. It's like checking how height, color, and shape are all passed down, leading to many different combinations in the offspring.

🎯 Exam Tip: While complex, a trihybrid cross essentially applies Mendel's laws independently to each of the three traits, leading to the 27:9:9:9:3:3:3:1 phenotypic ratio in the F₂ generation.

 

Question 8. What traits are determined by multiple alleles?
Answer: Multiple alleles refer to situations where more than two different versions of a gene exist in a population, although an individual can only inherit two of them (one from each parent). These multiple alleles can determine a single trait, leading to a wider range of phenotypes than simple dominant-recessive inheritance. A classic example is the human ABO blood group system. Blood type is determined by three alleles: I^A, I^B, and i. I^A and I^B are co-dominant, and both are dominant over i (recessive). This combination allows for four main blood types: A (I^AI^A or I^Ai), B (I^BI^B or I^Bi), AB (I^AI^B), and O (ii). This shows that a single trait, like blood type, can have multiple allelic forms, increasing genetic diversity within a population.
In simple words: Multiple alleles mean there are more than two versions of a gene that control one trait. Human blood type is a good example, with three different gene versions deciding your blood type.

🎯 Exam Tip: When discussing multiple alleles, always use the human ABO blood group system as a prime example, as it clearly illustrates co-dominance and dominance relationships.

 

Question 9. What is a gene?
Answer: A gene is the basic unit of heredity, acting as a functional segment of DNA that carries specific instructions for building a protein or a functional RNA molecule. Genes are responsible for transmitting biochemical, anatomical, and behavioral traits from parents to their offspring. They are located at specific positions (loci) on chromosomes. Each gene contains the code that determines particular characteristics, playing a crucial role in an organism's development, function, and unique features. For example, a gene might carry the code for eye color or blood type.
In simple words: A gene is a tiny instruction manual inside our DNA that tells our body what traits to have, like eye color, and passes these traits from parents to children.

🎯 Exam Tip: Define a gene as a functional unit of inheritance, emphasizing its role in coding for proteins/RNA and transmitting traits.