GSEB Class 12 Biology Solutions Chapter 5 Principles of Inheritance and Variation

Question 1. Mention the advantages of selecting pea plant for the experiment by Mendel.
Answer: Gregor Mendel chose the pea plant for his experiments due to several beneficial characteristics:
- It exhibits a wide range of varieties.
- Pure lines of this plant were readily available.
- The plant is compact, and its flowers are sufficiently large for manual manipulation.
- Pea flowers are bisexual and capable of producing fertile hybrids.
- Each plant yields a substantial number of seeds.
- The plants are naturally self-pollinating but can also be cross-pollinated.
- It is an annual plant with a short growth cycle of just a few months.
- The risk of unintended contamination during experiments is very low.
In simple words: Mendel chose pea plants because they have many distinct traits, are easy to breed, produce many offspring quickly, and can be controlled for pollination, making them ideal for studying inheritance.

🎯 Exam Tip: When listing advantages, focus on both observable traits (varieties, seed number) and practical experimental benefits (pollination control, short life cycle) to demonstrate comprehensive understanding.

Question 2. Differentiate between the following:
a. Dominance and Recessive
b. Homozygous and Heterozygous
c. Monohybrid and Dihybrid.
Answer:
a. In Mendel's law of dominance experiments, the trait that is expressed is termed the dominant character or dominance, while the trait that remains unexpressed or hidden is called the recessive character or recessiveness.
b. An individual is considered homozygous when its chromosomes carry identical genes for a specific character. Conversely, an individual is heterozygous if its chromosomes possess different genes for the same character.
c. A monohybrid cross involves two plants that differ in only one pair of contrasting characters. A dihybrid cross, on the other hand, involves two plants differing in two pairs of contrasting characters.
In simple words: Dominant traits show up, recessive traits hide. Homozygous means identical genes for a trait, heterozygous means different genes. Monohybrid tracks one trait, dihybrid tracks two.

🎯 Exam Tip: For differentiation questions, clearly define each term and provide a concise comparison point for full marks. Using examples can further strengthen your answer.

Question 3. A diploid organism is heterozygous for 4 loci, how many types of gametes can be produced?
Answer: The number of different types of gametes produced by a diploid organism heterozygous for 'n' loci can be calculated using the formula \(2^n\).
Here, n = Number of loci = 4.
So, the number of gametes = \(2^4\)
\( \implies 2 \times 2 \times 2 \times 2 = 16\) types of gametes.
In simple words: For every gene an organism has two different versions (heterozygous), it doubles the possible types of gametes it can make. With 4 such genes, it can make \(2 \times 2 \times 2 \times 2 = 16\) different gametes.

🎯 Exam Tip: Remember the formula \(2^n\) for calculating gamete types from heterozygous loci. Clearly showing the substitution and calculation steps is crucial.

Question 4. Explain the Law of Dominance using a monohybrid cross.
Answer: The Law of Dominance states that when a pair of contrasting factors (alleles) for a character are present together in an individual, only one of them, the dominant allele, expresses itself, while the other, the recessive allele, remains unexpressed. This principle helps explain why only one parental character appears in the \(F_1\) generation of a monohybrid cross, and how both parental characters reappear, typically in a 3:1 ratio, in the \(F_2\) generation.
In simple words: When two different versions of a gene are present, only the dominant one shows up. This explains why certain traits disappear in the first generation and then reappear in a specific ratio in the second generation.

🎯 Exam Tip: To explain the Law of Dominance, define it clearly and connect it directly to the observable phenotypic ratios in both the \(F_1\) and \(F_2\) generations of a monohybrid cross.

Question 5. Define and design a test-cross.
Answer: A test cross is a breeding experiment where an individual exhibiting a dominant phenotype, but of unknown genotype, is crossed with a homozygous recessive individual. This cross helps determine if the dominant parent is homozygous or heterozygous.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख एक टेस्ट क्रॉस को दर्शाता है। इसमें \(F_1\) संकर (जिसका जीनोटाइप Tt है, जहां T लंबापन दर्शाता है और t बौनापन दर्शाता है) को उसके अप्रभावी जनक (जिसका जीनोटाइप tt है) के साथ क्रॉस किया जाता है। आरेख दिखाता है कि Tt जनक से T और t युग्मक बनते हैं, जबकि tt जनक से केवल t युग्मक बनते हैं। इन युग्मकों के संयोजन से Tt (लंबा) और tt (बौना) संताने प्राप्त होती हैं।
In simple words: A test cross is when you breed an organism with a dominant trait (but unknown genetic makeup) with an organism that has the recessive trait. This helps figure out the genetic makeup of the unknown parent.

🎯 Exam Tip: Remember that the key to a test cross is crossing with a *homozygous recessive* individual. Be prepared to draw or describe the expected outcomes for both homozygous dominant and heterozygous test parents.

Question 6. Using a Punnett Square, work out the distribution of phenotypic features in the first filial generation after a cross between a homozygous female and a heterozygous male for a single locus.
Answer: Let's consider a single locus where 'T' represents the dominant allele (e.g., tallness) and 't' represents the recessive allele (e.g., dwarfness).
Homozygous female genotype: TT
Heterozygous male genotype: Tt
Cross: TT(♀) × Tt(♂)
ℹ️ चित्र व्याख्या (Diagram Explanation): यह पुनेट वर्ग एक एकल स्थान पर समयुग्मजी मादा (TT) और विषमयुग्मजी नर (Tt) के बीच एक क्रॉस को दर्शाता है। मादा TT से केवल 'T' युग्मक बनते हैं, जबकि नर Tt से 'T' और 't' युग्मक बनते हैं। पुनेट वर्ग में इन युग्मकों के संयोजन से \(F_1\) पीढ़ी के जीनोटाइप TT और Tt उत्पन्न होते हैं, जिससे सभी संताने लंबी या प्रभावी लक्षण वाली होती हैं।
From the Punnett square, the \(F_1\) generation offspring genotypes are:
- TT (Homozygous dominant)
- Tt (Heterozygous)
All offspring, whether TT or Tt, will exhibit the dominant phenotypic feature (e.g., tallness). Therefore, the phenotypic distribution in the \(F_1\) generation is 100% dominant trait.
In simple words: When a pure dominant female crosses with a mixed (heterozygous) male, all their children will show the dominant trait, even if some carry the hidden recessive gene.

🎯 Exam Tip: When constructing a Punnett square, correctly identify the gametes produced by each parent and systematically combine them. Clearly state both the genotypic and phenotypic ratios in the final answer.

Question 7. When a cross is made between a tall plant with the yellow seed (TtYy) and a tall plant with the green seed (Ttyy), what proportions of phenotype in the offspring could be expected to be
a. tall and green.
b. dwarf and green.
Answer: Let T = Tall, t = Dwarf; Y = Yellow, y = Green.
Parent 1: Tall plant with yellow seed (TtYy)
Parent 2: Tall plant with green seed (Ttyy)
This is a dihybrid cross. To find the proportions, we can analyze each character independently and then combine.
For height (Tt x Tt):
- Tall (TT, Tt) = 3
- Dwarf (tt) = 1
For seed color (Yy x yy):
- Yellow (Yy) = 1
- Green (yy) = 1
Now, combine these ratios:
a. Tall and green: (Tall proportion) x (Green proportion) = 3 x 1 = 3
b. Dwarf and green: (Dwarf proportion) x (Green proportion) = 1 x 1 = 1
Therefore, the expected phenotypic proportions are:
Tall and green = 3
Dwarf and green = 1
In simple words: When crossing specific tall-yellow and tall-green plants, we can predict that for every 3 tall-green offspring, there will be 1 dwarf-green offspring, by looking at each trait separately.

🎯 Exam Tip: For dihybrid crosses, analyze the inheritance of each trait separately before combining the probabilities. This simplifies complex crosses into two monohybrid problems.

Question 8. Two heterozygous parents are crossed. If the two loci are linked what would be the phenotypic features in \(F_1\) generation for a dihybrid cross?
Answer: When two heterozygous parents are crossed and the two loci are linked, the parental phenotypes appear in the \(F_1\) generation in much higher proportion than expected by independent assortment. This is a direct consequence of genetic linkage and the absence of independent assortment, meaning the genes tend to be inherited together rather than sorting independently into gametes.
In simple words: If two genes are linked (close together on the same chromosome) and parents are heterozygous, their children will mostly show combinations of traits similar to the parents, rather than new mixtures.

🎯 Exam Tip: Emphasize that linkage disrupts Mendelian independent assortment, leading to a higher frequency of parental phenotypic combinations and fewer recombinant types in the progeny.

Question 9. Briefly mention the contribution of T.H. Morgan in genetics.
Answer: Thomas Hunt Morgan was a distinguished geneticist who was awarded the Nobel Prize for his groundbreaking contributions to genetics. His key contributions include:
- He identified the fruit fly (Drosophila melanogaster) as an excellent experimental organism due to its ease of rearing and rapid multiplication.
- He conclusively established that genes are located on chromosomes.
- He elucidated the principles of linkage and crossing over.
- He discovered the phenomenon of sex linkage.
- He observed and documented genetic mutations.
- He developed the technique for chromosome mapping.
- He authored the influential book "The Theory of the Gene."
In simple words: T.H. Morgan was a Nobel Prize winner who proved that genes are on chromosomes using fruit flies. He also discovered linkage, crossing over, and sex linkage, laying foundations for genetic mapping.

🎯 Exam Tip: When discussing scientists' contributions, list their key discoveries or methodologies. For Morgan, emphasize his use of *Drosophila*, discovery of *linkage* and *sex linkage*, and establishment of the *chromosomal theory of inheritance*.

Question 10. What is pedigree analysis? Suggest how such an analysis can be useful.
Answer: Pedigree analysis involves the study of the inheritance patterns of specific characteristics across several generations within a family. This method is incredibly valuable in human genetics because humans have a long generation time and produce a relatively small number of offspring, making direct experimental genetic studies challenging. In pedigree analysis, the transmission of a particular trait is tracked through multiple generations, and the ancestral history of an individual is compiled into a family tree. This comprehensive data allows researchers to study the appearance and prevalence of traits within a given family line over many past generations.
In simple words: Pedigree analysis is like drawing a family tree to track how traits or diseases are passed down through generations. It's useful for human genetics because we can't do breeding experiments, so it helps us understand inherited patterns.

🎯 Exam Tip: Define pedigree analysis as a multi-generational study of trait inheritance. Highlight its utility for human genetics due to long generation times and small family sizes, and its role in tracking genetic disorders.

Question 11. How is sex determined in human beings?
Answer: In humans, out of the 23 pairs of chromosomes, 22 pairs are identical in both males and females; these are called autosomes and determine bodily characteristics other than sex. The remaining pair, the sex chromosomes, determines gender. Human females possess two X chromosomes (XX), whereas males have one X and one Y chromosome (XY).
During spermatogenesis, males (heterogametic) produce two types of sperm: 50 percent carry an X chromosome, and 50 percent carry a Y chromosome. Females (homogametic), however, produce only one type of egg, each carrying an X chromosome.
The sex of the offspring is determined by the sperm that fertilizes the egg:
- If an X-carrying sperm fertilizes the egg, the resulting zygote will be XX, developing into a female.
- If a Y-carrying sperm fertilizes the egg, the resulting zygote will be XY, developing into a male.
Thus, in every pregnancy, there is always a 50 percent probability of conceiving either a male or a female child. It is unfortunate that, historically, society has often blamed and mistreated females for producing female children, a misconception contradicted by genetic facts.
In simple words: A baby's sex is decided by the father's sperm. Females provide only X chromosomes, while males provide either X or Y. An X sperm makes a girl (XX), and a Y sperm makes a boy (XY), meaning there's always a 50/50 chance for either sex.

🎯 Exam Tip: Clearly state the chromosomal differences between males (XY) and females (XX). Emphasize that the male's sperm determines the sex due to its ability to carry either an X or Y chromosome, ensuring to mention the 50% probability for each sex.

Question 12. A child has blood group O. If the father has blood group A and mother blood group B, work out the genotypes of the parents and the possible genotypes of the other offspring.
Answer:
Since the child has blood group O (genotype \(i i\)), and blood group O is recessive, both parents must carry the 'i' allele.
Father has blood group A, so his genotype must be \(I^A i\).
Mother has blood group B, so her genotype must be \(I^B i\).
Parents' genotypes: Father \(I^A i\) × Mother \(I^B i\)
ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख एक पुनेट वर्ग को दर्शाता है जो रक्त समूह A वाले पिता (\(I^A i\)) और रक्त समूह B वाली माँ (\(I^B i\)) के बीच एक क्रॉस को दिखाता है। पिता से \(I^A\) और \(i\) युग्मक बनते हैं, और माँ से \(I^B\) और \(i\) युग्मक बनते हैं। उनके संयोजन से \(F_1\) पीढ़ी में \(I^A I^B\) (AB रक्त समूह), \(I^A i\) (A रक्त समूह), \(I^B i\) (B रक्त समूह), और \(i i\) (O रक्त समूह) के बच्चे पैदा हो सकते हैं।
Possible offspring genotypes from this cross:
\(I^A I^B\) (Blood Group AB)
\(I^A i\) (Blood Group A)
\(I^B i\) (Blood Group B)
\(i i\) (Blood Group O)
The other possible genotypes for their offspring, besides blood group O, are \(I^A I^B\) (AB blood group), \(I^A i\) (A blood group), and \(I^B i\) (B blood group).
In simple words: If a child has blood group O and the parents have A and B, it means both parents carry the hidden O gene. Their other children could have A, B, AB, or O blood types.

🎯 Exam Tip: When solving blood group problems, always deduce parental genotypes first, especially if an 'O' group child is present, as this indicates both parents must carry the 'i' allele. Then, use a Punnett square to systematically determine all possible offspring genotypes and phenotypes.

Question 13. Explain the following terms with examples.
a. Co-dominance
b. Incomplete dominance
Answer:
a. Co-dominance: This phenomenon occurs when two different alleles for the same gene both lack a dominant-recessive relationship and simultaneously express their effects in the heterozygous individual. As a result, both traits are distinctly visible. A classic example is the \(I^A\) and \(I^B\) alleles in human AB blood group, where both A and B antigens are produced.
b. Incomplete dominance: This is a phenomenon where neither of the two alleles of a gene is completely dominant over the other. When both alleles are present together in a heterozygote, they produce an intermediate phenotype that is distinct from either homozygous parent. Examples include flower color in Snapdragon (Antirrhinum majus) and the 4 o'clock plant (Mirabilis jalapa), where a cross between red and white flowers produces pink flowers.
In simple words: Co-dominance is when both versions of a gene show up fully (like AB blood type). Incomplete dominance is when they mix to create a new, intermediate trait (like pink flowers from red and white parents).

🎯 Exam Tip: Distinguish clearly between co-dominance and incomplete dominance by focusing on the expression of alleles in heterozygotes: co-dominance shows *both* phenotypes distinctly, while incomplete dominance results in an *intermediate* phenotype. Provide a specific example for each.

Question 14. What is point mutation? Give one example.
Answer: A point mutation, also known as a gene mutation, refers to any change occurring in the basic structure of a single gene, typically involving a single nucleotide base pair. These changes can alter the sequence of amino acids in a protein or affect gene expression. An illustrative example of a point mutation is Sickle cell anemia, where a single base substitution in the hemoglobin gene leads to an altered amino acid and deformed red blood cells.
In simple words: A point mutation is a tiny change in a gene, like swapping one letter in a word. A good example is sickle cell anemia, caused by just one wrong letter in the DNA code for hemoglobin.

🎯 Exam Tip: Define point mutation as a change in a single gene's structure or nucleotide sequence. Using Sickle cell anemia as an example is excellent, as it clearly demonstrates the impact of a single-base change.

Question 15. Who had proposed the chromosomal theory of inheritance?
Answer: The chromosomal theory of inheritance was proposed by Sutton and Boveri.
In simple words: Sutton and Boveri came up with the idea that genes are located on chromosomes and that these chromosomes are responsible for passing traits from parents to offspring.

🎯 Exam Tip: Accurately recall the names of scientists associated with major genetic theories. Sutton and Boveri are key figures for the chromosomal theory.

Question 16. Mention any two autosomal genetic disorders with their symptoms.
Answer: Here are two autosomal genetic disorders with their respective symptoms:
(i) Down's syndrome: This is an autosomal abnormality first described by Langdon Down in 1866. Individuals with Down's syndrome typically have 47 chromosomes instead of the usual 46. This condition results from the presence of an extra copy of chromosome 21, meaning chromosome 21 is triplicated (trisomy 21). The genetic makeup is often represented as 45A + XX (for females) or 45A + XY (for males), where 'A' denotes autosomes. Symptoms commonly include intellectual disability, characteristic facial features, and developmental delays.
(ii) Edward's syndrome: This disorder is caused by autosomal trisomy of chromosome 18. Babies born with Edward's syndrome often present with multiple severe skeletal defects, a small and malformed sternum, significant cardiac abnormalities, and abnormal kidneys, among other issues. The incidence of this syndrome is approximately 1 in 15,000 live births, and maternal age is a known factor influencing its occurrence.
In simple words: Down's syndrome is when there's an extra chromosome 21, causing developmental issues. Edward's syndrome is an extra chromosome 18, leading to severe physical and organ defects.

🎯 Exam Tip: For genetic disorders, always specify the chromosomal anomaly (e.g., trisomy, specific chromosome number) and list at least two distinct, recognizable symptoms. Mentioning the discoverer or incidence can add value.

Additional Important Questions And Answers

Question 1. Match the following.

A	B
a. Mendel	Chromosome theory
b. Karl Landsteiner	Genetics
c. Sutton and Boveri	Polytene chromosome
d. Morgan	Incomplete dominance
e. Bateson	Blood groups

Answer:

A	B
a. Mendel	Incomplete dominance
b. Karl Landsteiner	Blood groups
c. Sutton and Boveri	Chromosome theory
d. Morgan	Polytene chromosome
e. Bateson	Genetics

In simple words: This match-the-column exercise links key geneticists and their major contributions or associated concepts. For example, Mendel is associated with the foundational laws of inheritance, while Karl Landsteiner discovered blood groups.

🎯 Exam Tip: For matching questions, a strong understanding of the historical context and major contributions of key scientists in genetics is essential. Review the core discoveries associated with each name.

Question 2. a. Name the phenomenon of co-existence of two or more genes in same chromosome, b. Mention its types.
Answer:
a. The phenomenon where two or more genes reside on the same chromosome and tend to be inherited together is called **Linkage**.
b. The types of linkage are:
- **Complete linkage:** In this form, two or more genes or traits are consistently inherited together over many generations. This pattern is notably observed in male Drosophila, where crossing over does not occur between linked genes.
- **Incomplete linkage:** Here, linked genes can sometimes separate, leading to the formation of new combinations (recombinants). This occurs when crossing over happens between the linked genes. Incomplete linkage is observed in female Drosophila, where recombination is possible.
In simple words: Linkage is when genes on the same chromosome are inherited together. Complete linkage means they always stick together, while incomplete linkage means they can sometimes split apart through a process called crossing over.

🎯 Exam Tip: Define linkage as genes on the same chromosome. Differentiate complete from incomplete linkage by the presence or absence of recombination (crossing over), and remember specific examples like *Drosophila* sexes.

Question 3. What is Genetics?
Answer: Genetics is the branch of biology dedicated to the study of heredity and variation. It explores how characters are passed from parents to offspring and how differences arise among individuals.
In simple words: Genetics is the study of how traits are passed down from parents to children and why individuals within a family can be different from each other.

🎯 Exam Tip: A concise definition of genetics should always include both "heredity" (inheritance) and "variation" (differences) as its core components.

Question 4. Write the symptoms of
Haemophilia
Cystic fibrosis
Sickle cell anemia
Colour blindness
Thalassemia
Answer:
- Haemophilia - Blood clotting is impaired, leading to prolonged bleeding from even minor injuries.
- Cystic fibrosis - This is an inherited disease affecting secretory glands, causing the production of thick, sticky mucus that clogs organs like the lungs and pancreas, and also abnormal sweat glands.
- Sickle cell anemia - Red blood cells become sickle-shaped, which reduces their oxygen-carrying capacity and causes blockages in blood vessels.
- Colour blindness - Individuals are unable to distinguish between certain colors, most commonly red and green.
- Thalassemia - Characterized by a reduced production of hemoglobin or its complete absence, leading to anemia.
In simple words: Haemophilia causes blood not to clot. Cystic fibrosis thickens body secretions. Sickle cell anemia distorts red blood cells. Color blindness makes distinguishing colors hard. Thalassemia reduces hemoglobin production.

🎯 Exam Tip: When describing symptoms of genetic disorders, provide a clear, concise effect or characteristic for each. Focus on the primary physiological impact or observable trait.

Question 5. The following are the symbols shown in pedigree analysis. Identify them.
a. [square]
b. [circle]
c. [unfilled square]
d. [filled circle]
Answer: The symbols in pedigree analysis represent:
a. Mating between relatives (Consanguineous marriage - indicated by a double line connecting the male and female symbols).
b. Female (unaffected) - represented by an unfilled circle.
c. Male (unaffected) - represented by an unfilled square.
d. Affected female - represented by a filled circle.
In simple words: In a family tree for genetics (pedigree), a square is a male, a circle is a female. A filled shape means they have the trait, and a line between two shapes means they had children. A double line means they are related.

🎯 Exam Tip: Memorize the standard symbols used in pedigree analysis, especially those for male, female, affected/unaffected individuals, mating, and consanguineous marriage. Accurate identification is key for interpreting pedigrees.

Question 6. Complete the flowchart on the criss-cross inheritance seen in human beings.
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह फ्लोचार्ट मानवों में क्रिस-क्रॉस या ज़िग-ज़ैग वंशागति को दिखाता है, विशेष रूप से हीमोफिलिया जैसे एक्स-लिंक्ड विकारों के लिए। इसमें एक सामान्य माँ (XX HH) और एक हीमोफिलिक पिता (Xh Y) के बीच क्रॉस को दर्शाया गया है। उनके संतानों में बेटियाँ (X H Xh - कैरियर) और बेटे (X H Y - सामान्य) होते हैं। यह दिखाता है कि कैसे विकार पिता से पुत्री और फिर पुत्री से उसके पुत्र तक जा सकता है।
Based on the typical criss-cross inheritance pattern (e.g., for X-linked recessive disorders like Haemophilia), the flowchart is completed as follows:
Parents: Mother (Normal) XX HH x Father (Haemophilic) X^hY
Son-in-law (Normal) X^HY x Daughter (Carrier) X^HX^h
Resulting offspring:
(c) Daughter (Normal) X^HX^H
(d) Daughter (Carrier) X^HX^h
(e) Son (Normal) X^HY
(f) Son (Haemophilic) X^hY
In simple words: Criss-cross inheritance means a trait, often from the X chromosome, passes from a father to his daughter, and then from that daughter to her son. It skips a generation and affects males more.

🎯 Exam Tip: When completing a flowchart for criss-cross inheritance, understand that the trait typically passes from father to daughter (who becomes a carrier) and then from the daughter to her son. Use appropriate genotype notation (e.g., \(X^H\) for normal, \(X^h\) for affected).

Question 7. Note the relationship between the first two words and suggest a suitable word for the 4th place.
a. Genetics - Bateson :: Genes -
b. Visible characters of an organism - Phenotype :: Genetic constitution of an organism -
c. Epigenesis - Wolf :: Blending inheritance -
d. Multiple alleles - Blood group :: Polygenic traits -
e. Heredity - Resemblance between parents and offspring :: Variation -
f. Garden pea - Pisum sativum :: Sweet pea -
g. Monohybrid ratio - 3:1 :: Dihybrid ratio -
Answer:
a. Genetics - Bateson :: Genes - **Johannsen** (Bateson coined 'genetics'; Johannsen coined 'gene')
b. Visible characters of an organism - Phenotype :: Genetic constitution of an organism - **Genotype** (Phenotype is observable traits; Genotype is genetic makeup)
c. Epigenesis - Wolf :: Blending inheritance - **Galton** (Wolf proposed epigenesis; Galton supported blending inheritance)
d. Multiple alleles - Blood group :: Polygenic traits - **Skin colour** (Blood group is an example of multiple alleles; Skin color is an example of polygenic traits)
e. Heredity - Resemblance between parents and offspring :: Variation - **Difference between parents and offspring** (Heredity describes similarities; Variation describes differences)
f. Garden pea - Pisum sativum :: Sweet pea - **Lathyrus odoratus** (Pisum sativum is the scientific name for garden pea; Lathyrus odoratus is for sweet pea)
g. Monohybrid ratio - 3:1 :: Dihybrid ratio - **9:3:3:1** (3:1 is the phenotypic ratio for a monohybrid cross; 9:3:3:1 is for a dihybrid cross)
In simple words: This question asks you to complete analogies related to genetic terms and historical figures. You need to identify the relationship in the first pair to find the correct match for the second pair.

🎯 Exam Tip: For analogy questions, analyze the relationship (e.g., inventor-invention, concept-example, concept-opposite) in the given pair to accurately determine the missing term's relationship in the second pair.

Question 8. Find out the odd one in each group.
a. 3:1, 1:2:1, 9:3:3:1, 9:7
b. Homozygous, Heterozygous, Hemizygous, Azygous
c. Monohybrid, Dihybrid, Polyhybrid, Back cross
d. Tall, Axial, Purple, White
Answer:
a. **9:7** (All others - 3:1, 1:2:1, 9:3:3:1 - are standard Mendelian or modified Mendelian ratios that are variations of 16 parts, whereas 9:7 is a modified dihybrid ratio, often for complementary genes.)
b. **Azygous** (Homozygous, heterozygous, and hemizygous describe the state of alleles at a gene locus. Azygous, meaning "without a zygote" or single, is not a standard term for gene allelic combinations.)
c. **Back cross** (Monohybrid, dihybrid, and polyhybrid refer to types of crosses based on the number of character pairs being studied. A back cross is a specific type of cross used to determine parental genotype, not a classification based on character pairs.)
d. **White** (Tall, Axial, and Purple are typically dominant traits for pea plants (or traits that can be dominant). White could be a recessive trait or a flower color, but in the context of Mendelian traits, it stands out as a color description rather than a general descriptor of a plant characteristic like position or height.)
In simple words: The odd ones out are 9:7 (a specific ratio), Azygous (not a genetic term for allele states), Back cross (a type of cross, not a classification by number of traits), and White (a color, not a general trait like tallness or axial position).

🎯 Exam Tip: To identify the odd one out, understand the common category or characteristic shared by the majority of items. The odd one will not fit this established pattern or classification.

Question 9. What is a monohybrid cross?
Answer: A monohybrid cross is a genetic cross conducted between individuals of a species where the inheritance of only one pair of contrasting characters is considered. For instance, crossing a tall pea plant with a dwarf pea plant to study only the inheritance of height.
In simple words: A monohybrid cross is a breeding experiment where scientists track how only one specific trait, like height or flower color, is passed from parents to offspring.

🎯 Exam Tip: Define a monohybrid cross by its focus on *one* pair of contrasting characters. This distinction is crucial for understanding basic Mendelian inheritance.

Question 10. Name a plant that shows incomplete dominance in respect to the colour of its flowers.
Answer: The plant that exhibits incomplete dominance in the color of its flowers is Mirabilis jalapa, commonly known as the 4 o'clock plant.
In simple words: The 4 o'clock plant (Mirabilis jalapa) shows incomplete dominance in its flower color, meaning crossing red and white flowers results in pink flowers, not just red or white.

🎯 Exam Tip: Remember Mirabilis jalapa (4 o'clock plant) or Snapdragon as classic examples of incomplete dominance in flower color, as they produce an intermediate phenotype (pink) from red and white parents.

Question 11. A heterozygous tall plant is crossed with a homozygous dominant plant. What is the result in \(F_1\) generations? Explain with adequate illustration.
Answer: Let's assume 'T' represents the allele for tallness (dominant) and 't' represents the allele for dwarfness (recessive).
Heterozygous tall plant genotype: Tt
Homozygous dominant plant genotype: TT
The cross is: Tt × TT
ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख एक विषमयुग्मजी लंबे पौधे (Tt) और एक समयुग्मजी प्रभावी लंबे पौधे (TT) के बीच एक क्रॉस को दर्शाता है। Tt जनक से T और t युग्मक बनते हैं, जबकि TT जनक से केवल T युग्मक बनते हैं। उनके संयोजन से \(F_1\) पीढ़ी में TT (समयुलग्मजी लंबा) और Tt (विषमयुग्मजी लंबा) जीनोटाइप वाले संताने उत्पन्न होती हैं।
Expected results in the \(F_1\) generation:
- 50% Homozygous tall plants (TT)
- 50% Heterozygous tall plants (Tt)
Phenotypically, all plants in the \(F_1\) generation will be tall.
In simple words: When a mixed-tall plant is crossed with a pure-tall plant, all offspring will appear tall. Half will be purely tall genetically, and half will be tall but carry the dwarf gene.

🎯 Exam Tip: Clearly define the alleles and parental genotypes. Use a Punnett square to show the gamete combinations and then state both the genotypic and phenotypic ratios accurately for the \(F_1\) generation.

Question 12. Name the scientists who rediscovered Mendelism.
Answer: The scientists credited with independently rediscovering Mendel's laws of inheritance were Correns (Germany), De Vries (Holland), and Tshermak (Austria).
In simple words: Three scientists-Correns, De Vries, and Tshermak-independently rediscovered Mendel's work on inheritance around the turn of the 20th century.

🎯 Exam Tip: Remember the three key scientists – Correns, De Vries, and Tshermak – who independently confirmed Mendel's findings in the early 1900s.

Question 13. What do you understand from the following flow chart?
ℹ️ चित्र व्याख्या (Diagram Explanation): यह फ्लोचार्ट एक संकर परीक्षण क्रॉस को दर्शाता है जिसमें एक विषमयुग्मजी पीले बीज वाले पौधे (Yy, प्रभावी लक्षण) को एक समयुग्मजी अप्रभावी हरे बीज वाले पौधे (yy, अप्रभावी जनक) के साथ क्रॉस किया गया है। यह दिखाता है कि Yy जनक से Y और y युग्मक बनते हैं, जबकि yy जनक से केवल y युग्मक बनते हैं। परिणामस्वरूप, \(F_1\) पीढ़ी में 50% Yy (पीले बीज वाले) और 50% yy (हरे बीज वाले) पौधे होते हैं।
Answer: The provided flow chart visually represents a monohybrid test cross. It demonstrates a cross between a heterozygous yellow-seeded plant (Yy) and a homozygous recessive green-seeded plant (yy). The outcome shows an equal distribution (50% Yy, 50% yy) of phenotypes in the offspring, which is characteristic of a test cross to determine the genotype of the dominant parent.
In simple words: The chart shows a test cross where a plant with an unknown dominant trait (yellow seeds) is crossed with a plant showing the recessive trait (green seeds). The results (50% yellow, 50% green) confirm the dominant parent was heterozygous.

🎯 Exam Tip: When analyzing flowcharts or diagrams, identify the parents, gametes, and offspring genotypes/phenotypes. For a test cross, note the use of a homozygous recessive parent and the characteristic 1:1 ratio if the dominant parent is heterozygous.

Question 14. What do the following genetic symbols mean? Aa, AA
Answer: In genetics, these symbols represent:
- **Aa:** This genotype signifies a **heterozygous** individual, meaning they possess two different alleles for a particular gene (one dominant 'A' and one recessive 'a').
- **AA:** This genotype denotes a **homozygous dominant** individual, indicating they have two identical dominant alleles ('A' and 'A') for a specific gene.
In simple words: 'Aa' means an organism has two different versions of a gene, while 'AA' means it has two identical dominant versions of that gene.

🎯 Exam Tip: Clearly define "heterozygous" as having two different alleles and "homozygous dominant" as having two identical dominant alleles. Accuracy in genetic terminology is crucial.

Question 15. A man with blood group A marries a woman with blood group B. Their child has blood group O.
a. What are the genotypes of their parents?
b. What are the other genotypes and in what ratio would you expect in the offspring from this marriage?
Answer:
a. Since the child has blood group O (genotype \(I^O I^O\)), and this requires both parents to contribute an \(I^O\) allele, the genotypes of the parents must be:
- Father: Blood group A, so genotype is \(I^A I^O\).
- Mother: Blood group B, so genotype is \(I^B I^O\).
b. To determine the other genotypes and their ratio, we can perform a Punnett square for the cross \(I^A I^O \times I^B I^O\):
Gametes from Father: \(I^A\), \(I^O\)
Gametes from Mother: \(I^B\), \(I^O\)
Possible offspring genotypes and phenotypes:
- \(I^A I^B\): Blood group AB
- \(I^A I^O\): Blood group A
- \(I^B I^O\): Blood group B
- \(I^O I^O\): Blood group O
The other possible genotypes are \(I^A I^B\), \(I^A I^O\), and \(I^B I^O\). The expected phenotypic ratio in the offspring is 1 (AB) : 1 (A) : 1 (B) : 1 (O).
In simple words: Because they had a child with O blood, both the A and B blood group parents must carry the O gene. This means their children could have A, B, AB, or O blood types, each with an equal chance.

🎯 Exam Tip: For blood group inheritance, remember that type O is recessive (\(I^O I^O\)). If an O-group child is born to A and B parents, it implies both parents are heterozygous (\(I^A I^O\) and \(I^B I^O\)). Systematically list all possible genotypes and their corresponding phenotypes and ratios.

Question 16. Give reason.
a. Mendel selected garden pea (Pisum sativum) as his experimental plant.
b. Blood group identification is not required while transfusing serum.
Answer:
a. Mendel chose the garden pea (Pisum sativum) for his experiments due to a confluence of favorable characteristics. These include the presence of numerous clearly contrasting characters, the production of fertile hybrids, ease of cultivation, a short growth period and life cycle, and the ready availability of pure breeding varieties. All these factors made the garden pea an ideal model for studying inheritance patterns.
b. Blood group identification is not necessary when transfusing only serum because serum, which is the fluid component of blood after clotting factors and cells have been removed, does not contain any antigens (like A or B antigens) on its own. Antigens are located on the surface of red blood cells, which are absent in serum.
In simple words: Mendel used pea plants because they had many clear traits, grew fast, and were easy to control for breeding. Blood typing isn't needed for serum transfusions because serum lacks the red blood cell antigens that cause reactions.

🎯 Exam Tip: When providing reasons, ensure they are biologically sound and directly answer the "why" aspect of the question. For pea plants, focus on genetic and practical advantages. For serum, emphasize the absence of antigens.

Question 17. Give the scientific name and the common name of plant in which incomplete dominance was first discovered.
Answer: The plant in which incomplete dominance was first discovered is the Four O'clock plant, scientifically known as Mirabilis jalapa.
In simple words: Incomplete dominance was first found in the Four O'clock plant, whose scientific name is Mirabilis jalapa.

🎯 Exam Tip: Be precise with scientific names (capitalized genus, lowercase species, italicized) and common names. Mirabilis jalapa is a classic example for incomplete dominance.

Question 18. What does the letter Fx represent in heredity?
Answer: In the context of heredity, the letter \(F_x\) (often seen as \(F_1\), \(F_2\), etc.) represents the Filial generation. Specifically, \(F_1\) stands for the First Filial generation, which refers to the first generation of offspring resulting from a cross between two parental (P) individuals.
In simple words: In genetics, 'F' followed by a number (like \(F_1\) or \(F_2\)) refers to the generation of offspring after a cross, where \(F_1\) is the first generation of children.

🎯 Exam Tip: Know your genetic terminology. \(F_1\) and \(F_2\) are fundamental terms referring to the first and second filial generations, respectively, representing offspring in a cross.

Question 19. Match the related items from B and C with column A.
A- Blood groups
B - Antigens
C- Antibodies

A	B	C
A	B	A
B	A	B
AB	-	AB
O	AB	-

Answer:

A- Blood groups	B - Antigens	C- Antibodies
A	A	B
B	B	A
AB	AB	-
O	-	AB

In simple words: This table matches each human blood group with the specific antigens (markers) found on its red blood cells and the antibodies present in its plasma. For example, blood group A has A antigens and B antibodies.

🎯 Exam Tip: Clearly understand the relationship between blood group, antigens (on RBCs), and antibodies (in plasma). Remember that a person has antibodies against antigens they *do not* possess to prevent immune reactions.

Question 20. Identify the personality.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक दाढ़ी वाले व्यक्ति को दर्शाता है जो ग्रेगर जोहान मेंडल हैं, जिन्हें आनुवंशिकी के जनक के रूप में जाना जाता है। उन्होंने मटर के पौधों पर अपने प्रयोगों के माध्यम से आनुवंशिकता के मौलिक नियमों की खोज की।
Answer: The personality identified in the image is Gregor Johann Mendel, widely recognized as the Father of Genetics.
In simple words: The picture shows Gregor Johann Mendel, who is famously known as the Father of Genetics for his pioneering work on inheritance.

🎯 Exam Tip: Recognize iconic figures in science. Gregor Mendel's image should immediately bring to mind his contributions to genetics.

Question 21. What is the glycoprotein found on the RBC's of a person with blood group AB?
Answer: A person with blood group AB has both Glycoprotein A and Glycoprotein B found on the surface of their red blood cells.
In simple words: People with AB blood group have both 'A' and 'B' glycoproteins on their red blood cells.

🎯 Exam Tip: Remember that AB blood group individuals possess both A and B antigens (glycoproteins) on their red blood cells, making them universal recipients.

Question 22. Match the following.

A	B
i. Incomplete dominance	Punnet
ii. Polygenic traits	Blood groups
iii. Multiple alleles	Skin colour
iv. Checkerboard	Mirabilis jalapa

Answer:

A	B
i. Incomplete dominance	Mirabilis jalapa
ii. Polygenic traits	Skin colour
iii. Multiple alleles	Blood groups
iv. Checkerboard	Punnet

In simple words: This matching exercise connects genetic concepts with their examples or related terms. For instance, incomplete dominance is seen in Mirabilis jalapa, and a checkerboard refers to a Punnett square.

🎯 Exam Tip: For matching questions, ensure you know both definitions and classic examples for each genetic concept. "Checkerboard" is another name for a Punnett square.

Question 23. Mendel, in his last breath said 'Meine zeit word schoon kommen'. What is the meaning of it?
Answer: The phrase 'Meine zeit word schoon kommen' translates from German to English as "My time will come soon." This statement reflects Mendel's foresight and confidence that despite the lack of immediate recognition for his groundbreaking work during his lifetime, its significance would eventually be acknowledged.
In simple words: When Mendel said "My time will come soon" on his deathbed, he meant that he believed his scientific work, though not recognized at the time, would eventually be understood and appreciated in the future.

🎯 Exam Tip: Understanding the historical context of scientific discoveries, including personal statements like Mendel's, can provide valuable insight into the challenges and eventual triumphs of scientific progress.

Question 24. Give the scientific names of the following.
4 o'clock plant, Sweet pea, Snapdragon.
Answer:
- 4 o'clock plant: Mirabilis jalapa
- Sweet pea: Lathyrus odoratus
- Snapdragon: Antirrhinum majus
In simple words: The scientific names are Mirabilis jalapa for the 4 o'clock plant, Lathyrus odoratus for sweet pea, and Antirrhinum majus for snapdragon.

🎯 Exam Tip: Practice recalling the scientific names for common plants, especially those frequently used as examples in genetics, such as those demonstrating incomplete dominance (Mirabilis jalapa, Antirrhinum majus).

Question 25. Who discovered blood groups?
Answer: Blood groups were discovered by Karl Landsteiner in 1900.
In simple words: Karl Landsteiner discovered the different human blood groups in 1900.

🎯 Exam Tip: Associate Karl Landsteiner with the discovery of the ABO blood group system, a fundamental concept in human biology and medicine.

 

Question 26. Discuss under what conditions the ratio 9:3:3:1 is modified to 9:7 ratio.
Answer: The 9:3:3:1 ratio is altered to 9:7 when complementary gene action is involved.
In simple words: This specific genetic ratio change happens when two different genes work together to produce a single trait, and both genes need to be present in their dominant form for the full effect.

🎯 Exam Tip: Understanding gene interactions like complementary gene action is crucial for complex heredity problems; remember that such interactions modify Mendelian ratios.

 

Question 27. A plant with red flowers was crossed with another plant of the same species with white flowers. The offspring thus obtained were 60 plants with only pink flowers. On selling, these plants produced 60 plants with red flowers, 120 plants with pink flowers, and 60 with white flowers.
a. Name the genetic principle behind this.
b. Give a scientific explanation for this.
c. Name the geneticist who conducted this experiment.
Answer:
(a) The genetic principle demonstrated here is incomplete dominance.
(b) In balsam plants, incomplete dominance is observed. When a plant with red flowers is crossed with a plant with white flowers, the F1 generation produces offspring with a new phenotype-pink flowers-which is an intermediate blend of the parental traits. In the F2 generation, a cross among these pink-flowered plants yields red, pink, and white flowers in a 1:2:1 ratio (60 red, 120 pink, 60 white).
(c) Carl Correns performed this experiment.
In simple words: When red and white flowers cross to make pink flowers, it's called incomplete dominance because neither color is fully dominant. This pattern was studied by Correns.

🎯 Exam Tip: Recognize incomplete dominance by the appearance of an intermediate phenotype in the F1 generation and a 1:2:1 phenotypic ratio in the F2 generation.

 

Question 28. All test crosses are back cross. 'But all backcrosses are not test cross'. Justify the statement.
Answer: A test cross involves crossing an F1 hybrid with its recessive parent. A back cross, on the other hand, is the mating of an F1 hybrid with any of its parents (either dominant or recessive). Therefore, every test cross is a type of back cross (specifically, a back cross with the recessive parent), but not all back crosses are test crosses because they can also involve mating with the dominant parent.
In simple words: A test cross is always a back cross because it involves mating with a parent. However, a back cross isn't always a test cross because it can be with either the dominant or recessive parent, but a test cross specifically requires the recessive parent.

🎯 Exam Tip: Differentiating between test crosses and back crosses is vital for understanding genetic analysis; remember that a test cross is a specific type of back cross used to determine genotype.

 

Question 29. Copy and complete the checkerboard of the dihybrid cross. Write the genotypic and phenotypic ratios. Gametes are given.
Answer: Mendel utilized a Punnett square, also known as a checkerboard, to graphically illustrate the dihybrid cross. Let 'R' signify the gene for round seed shape and 'r' for wrinkled shape. Let 'Y' represent yellow seed color and 'y' represent green seed color. Thus, the genotype for a pure breeding round yellow plant is RRYY, and for a wrinkled green plant is rryy. The F1 hybrids (RrYy) produce four distinct types of gametes in equal proportions (RY, Ry, rY, ry).

ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख एक द्विसंकर क्रॉस के लिए पुनेट वर्ग को दर्शाता है. यह F1 पीढ़ी के पौधों से बने युग्मकों (RY, Ry, rY, ry) के संयोजन को दिखाता है और F2 पीढ़ी के विभिन्न जीनोटाइप और फेनोटाइप को प्रदर्शित करता है, जिससे स्वतंत्र वर्गीकरण का सिद्धांत स्पष्ट होता है.

♀ \(\Large \diagdown\) ♂	RY	Ry	rY	ry
RY	RRYY	RRYy	RrYY	RrYy
Ry	RRYy	RRyy	RrYy	Rryy
rY	RrYY	RrYy	rrYY	rrYy
ry	RrYy	Rryy	rrYy	rryy

From these 16 combinations, \( \frac{9}{16} \) are round yellow (possessing dominant genes R and Y), \( \frac{3}{16} \) are round green (having dominant R and recessive y), \( \frac{3}{16} \) are wrinkled yellow (with recessive r and dominant Y), and \( \frac{1}{16} \) is wrinkled green (with both recessive r and y). This gives the dihybrid phenotypic ratio of 9:3:3:1. The genotypic ratio is 1:2:1:2:4:2:1:2:1. In the dihybrid cross, the emergence of new combinations such as round green (Ry) and wrinkled yellow (rY) illustrates independent assortment. This law asserts that when multiple pairs of characters are involved in a cross, the factor pairs for each character segregate independently of one another.
In simple words: This problem uses a Punnett square to show how two traits, seed shape (round/wrinkled) and seed color (yellow/green), are inherited together. The F1 generation produces four types of gametes, and their combination in the F2 generation results in a 9:3:3:1 phenotypic ratio and a 1:2:1:2:4:2:1:2:1 genotypic ratio, demonstrating Mendel's law of independent assortment.

🎯 Exam Tip: Remember to clearly label gametes and genotypes in Punnett squares for dihybrid crosses, and always state both phenotypic and genotypic ratios as they are distinct scoring criteria.

 

Question 30. A test cross is used to identify whether the plant is homozygous or heterozygous. Justify this statement.
Answer: To determine the genetic makeup (purity) of a plant, one performs a test cross. If the unknown plant is homozygous dominant, crossing it with a recessive parent will result in progeny that are all of a single phenotype (dominant). If the unknown plant is heterozygous, the test cross will produce two types of progeny in a 1:1 ratio (dominant and recessive phenotypes).
In simple words: A test cross helps figure out if a plant has two identical genes (homozygous) or two different genes (heterozygous) for a trait by crossing it with a recessive plant. If all offspring show the dominant trait, the unknown parent was homozygous dominant; if half show the dominant trait and half the recessive trait, the unknown parent was heterozygous.

🎯 Exam Tip: The ability to predict offspring ratios from a test cross is a key skill. Clearly distinguish the outcomes for homozygous versus heterozygous unknown parents.

 

Question 31. Note the relationship between the first two words and suggest a suitable word for the 4th place.
a. XX - XO mechanism - Grasshopper ::
XX - XY mechanism -
b. Sex limited inheritance - Beard in man ::
Sex influenced inheritance -
c. Phenylketonuria - Phenylalanine hydroxylase::
Alkaptonuria -
d. Down syndrome - Langdon Down::
Klinefelter's syndrome -
e. Turner's syndrome - 45 chromosomes::
Down's syndrome -
Answer:
(a) Man
(b) Baldness in man
(c) Homogentisic acid oxidase
(d) Harry Klinefelter
(e) 47 chromosomes
In simple words: This question tests your knowledge of genetic mechanisms, inheritance patterns, and genetic disorders by asking you to complete analogies.

🎯 Exam Tip: Review key geneticists and their discoveries, along with the defining characteristics and underlying causes of common genetic disorders and sex determination mechanisms.

 

Question 32. Find the odd one of the following.
a. Alkaptonuria, Phenylketonuria, Albinism, Colour blindness
b. Deletion, Duplication, Inversion, Conversion
c. Haploidy, Diploidy, Polyploidy, Polydactyly
d. Nullisomic, Monosomic, Polysomic, Polygenic
e. Klinefelter's syndrome, Down's syndrome, Turner's syndrome, Acquired Immune Deficiency syndrome.
Answer:
(a) Colour blindness
(b) Conversion
(c) Polydactyly
(d) Polygenic
(e) Acquired Immune Deficiency Syndrome
In simple words: For each group, you need to identify the term that doesn't fit with the others based on their genetic classification or nature.

🎯 Exam Tip: To answer "odd one out" questions effectively, quickly categorize the given terms (e.g., genetic disorders, chromosomal mutations, ploidy levels) and then pinpoint the outlier that doesn't share the common characteristic.

 

Question 33. Give reason.
a. Drosophila is the ideal material for genetic study.
b. Haemophilia is more common in males.
c. Aneuploidy leads to variation.
d. Sex of the child is determined by the father.
Answer:
(a) Drosophila, the fruit fly, is an excellent model organism for genetic studies because it reproduces rapidly, has a short generation time, produces many offspring, possesses only four pairs of chromosomes, and its chromosomes are easily distinguishable under a microscope.
(b) Haemophilia is an X-linked recessive disorder. Since males have only one X chromosome, they express the trait if they inherit the recessive allele on that X chromosome, making it more common in males than in females, who need two copies of the recessive allele to be affected.
(c) Aneuploidy, which is a chromosomal mutation, results in an abnormal number of chromosomes. This change in chromosome count directly leads to genetic variation, as it alters the gene dosage and can cause significant phenotypic effects.
(d) In humans, the sex of the child is determined by the father because males are heterogametic, producing two types of sperm: those carrying an X chromosome and those carrying a Y chromosome. Females, being homogametic, produce only eggs carrying an X chromosome. Thus, the type of sperm that fertilizes the egg dictates the offspring's sex.
In simple words: Drosophila is good for genetics due to its quick reproduction and few chromosomes. Males get hemophilia more often because it's linked to the X chromosome, and they only have one. Aneuploidy creates variation by changing chromosome numbers. The father determines a child's sex because he contributes either an X or a Y sperm.

🎯 Exam Tip: For "give reason" questions, provide a concise and scientifically accurate explanation. Focus on the genetic or biological principles underlying each statement.

 

Question 34. Construct a flow chart showing criss-cross inheritance.
Answer: Haemophilia, often called 'bleeder's disease', is a hereditary sex-linked blood disorder in humans. It was identified by John Otto in 1803. This condition arises from the absence of an antihaemophilic factor, leading to excessive bleeding even from minor injuries, which can be fatal. The disease was initially documented in the royal families of Europe, including Queen Victoria. The genes responsible for haemophilia are situated on the X chromosome; the Y chromosome does not carry genes for this trait. Haemophilia is caused by a recessive gene 'h', while the dominant gene 'H' controls normal blood clotting.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख हीमोफिलिया की क्रिस-क्रॉस या ज़िग-ज़ैग वंशागति को दिखाता है. इसमें दर्शाया गया है कि कैसे सामान्य माता (XXHH) और हीमोफिलिक पिता (XhY) के बच्चे होते हैं, जिनमें बेटियां वाहक (XXHh) होती हैं और बेटे सामान्य (XHY) होते हैं, जिससे यह स्पष्ट होता है कि रोग का वाहक कौन है और किसको रोग होने की संभावना है.

	Mother XXHH (normal)	x	Father XhY (haemophilic)
		\( \implies \)
Son-in-law XHY (normal)	x	Daughter XHXh (carrier)	Son XhY (haemophilic)

Females possess two X chromosomes and can have genotypes 'H H', 'H h', or 'h h'. Homozygous dominant females (HH) are normal. Heterozygous females (Hh) are carriers but not haemophilic, as 'H' is dominant over 'h'; they can pass the haemophilia allele to their sons. Homozygous recessive females (hh) will be haemophilic. When a normal woman (HH) marries a haemophilic man (h), their daughters (Hh) become carriers because the father transmits his X chromosome only to his daughters. Mothers, in turn, pass their X chromosomes to both sons and daughters. All sons are normal (H) since the Y chromosome from the father carries no gene for this trait. Haemophilia is transmitted from the father to the grandson through the daughter, a pattern known as criss-cross or zig-zag inheritance. X-linked recessive genes are expressed in homozygous conditions (hh) in females. In males, a single dose of the recessive gene 'h' on the X chromosome is enough for expression, making X-linked disorders more common in males.
In simple words: Haemophilia, an X-linked recessive disorder, is passed from a father to his grandson through his daughter (a carrier). This flow chart illustrates how a normal mother and a haemophilic father produce carrier daughters and normal sons, showing that the disease affects males more frequently due to their single X chromosome.

🎯 Exam Tip: When drawing genetic flowcharts, clearly indicate genotypes, phenotypes, and the sex of individuals. Emphasize the X-linked nature of the inheritance pattern and its implications for male versus female offspring.

 

Question 35. Observe the following diagrams and identify the different types of chromosomal mutation.
Answer:
(A) Deletion
(B) Duplication
(C) Inversion
(D) Translocation
In simple words: By looking at the provided diagrams, you can identify different ways chromosomes change, specifically deletion (part missing), duplication (part copied), inversion (part flipped), and translocation (part moved).

🎯 Exam Tip: For questions involving diagrams of chromosomal mutations, focus on the changes in gene order or presence. Understand the distinct visual characteristics of deletion, duplication, inversion, and translocation.

 

Question 36. Substitution of a wrong amino acid valine instead of glutamic acid in the 6th position of globin chain of RBC causes disease in man.
Answer:
(a) The disease caused by the substitution of valine for glutamic acid in the 6th position of the globin chain of RBC is Sickle cell anemia.
(b) Sickle cell anemia is a genetic disorder marked by sickle-shaped red blood cells (RBCs) and abnormal hemoglobin. It results from a gene mutation where valine replaces glutamic acid at the 6th position of the beta-globin chain. Under low oxygen conditions, these abnormal hemoglobin molecules aggregate, forming fiber-like structures that deform the RBC membrane, causing cells to become sickle-shaped and impairing their oxygen-carrying capacity. This defect, also known as 'sickle-cell crisis', leads to rapid destruction of these misshapen erythrocytes, resulting in anemia. The disease is controlled by a pair of alleles, HbA and HbS. Pedigree analysis reveals three genotypes (HbA HbA, HbA HbS, HbS HbS) and two phenotypes (normal and affected). Individuals with homozygous HbA HbA are normal, while those with HbS HbS are affected. Heterozygous individuals (HbA HbS) exhibit sickle cell trait; they are generally unaffected but carry one normal and one defective gene, capable of transmitting the latter to 50% of their offspring. The amino acid sequence for normal hemoglobin is valine, histidine, leucine, threonine, proline, glutamic acid, and for sickle cell hemoglobin is valine, histidine, leucine, threonine, proline, valine.
In simple words: The disease described is Sickle cell anemia, where a single amino acid change in hemoglobin causes red blood cells to become sickle-shaped, leading to anemia and other health problems. It's a genetic condition where carriers are generally healthy but can pass the gene on.

🎯 Exam Tip: When explaining genetic disorders like sickle cell anemia, ensure you mention the specific gene mutation, the resulting protein change, its effect on cell structure/function, and the mode of inheritance, including genotypes and phenotypes.

 

Question 37. Who proposed the mutation theory of heredity?
Answer: Hugo de Vries
In simple words: The idea that sudden changes in genes can cause new traits was proposed by Hugo de Vries.

🎯 Exam Tip: Associate key genetic theories with their discoverers; Hugo de Vries is famously linked to the mutation theory of heredity.

 

Question 38. Which one of the following is male Drosophila?
A
B
Answer:
(A) - male
(B) - Female
In simple words: Male Drosophila (A) is typically smaller with a darker, more rounded abdomen, while female Drosophila (B) is larger with a more pointed abdomen.

🎯 Exam Tip: When identifying Drosophila sexes, look for differences in size and the shape of the abdomen, with males generally being smaller and having a more rounded, darker tip.

 

Question 39. A man suffering from hemophilia marries a carrier woman. Work out the chances, of their progeny suffering from the disease. Use a flow chart/Punnet square.
Answer:

ℹ️ चित्र व्याख्या (Diagram Explanation): यह आरेख एक हीमोफिलिक पिता (XhY) और एक वाहक माता (XHXh) के बीच क्रॉस से उत्पन्न संतति में हीमोफिलिया की वंशागति को दिखाता है. इसमें पुत्रियों और पुत्रों दोनों में सामान्य, वाहक और हीमोफिलिक होने की संभावनाओं को दर्शाया गया है.

	Father (haemophilic) XhY		Mother (Carrier) XHXh
Gametes	Xh, Y		XH, Xh

♀ \(\Large \diagdown\) ♂	XH	Xh
Xh	XHXh (Carrier female)	XhXh (Haemophilic female)
Y	XHY (Normal male)	XhY (Haemophilic male)

50% of the progeny will be haemophilic and 50% of the progeny will be normal. Specifically, 25% of the offspring will be carrier females (XHXh), 25% haemophilic females (XhXh), 25% normal males (XHY), and 25% haemophilic males (XhY).
In simple words: When a man with hemophilia marries a carrier woman, there's a 50% chance their children will be affected by hemophilia. This cross can result in both carrier and haemophilic daughters, as well as normal and haemophilic sons.

🎯 Exam Tip: For sex-linked inheritance problems, always write out the genotypes clearly, paying attention to the X and Y chromosomes, and then use a Punnett square to determine the exact probabilities for each phenotype and genotype.

 

Question 40. Match the following.
Answer:

A	B
(a) Mutation theory	Hugo de Vries
(b) Chromosome map	Sturtevent
(c) Haemophilia	John Cotto
(d) Inborn errors of metabolism	Garrod

In simple words: This question asks you to match important genetic concepts and discoveries with the scientists who are credited with them.

🎯 Exam Tip: Memorizing the contributions of key scientists to the field of genetics is essential. Ensure you can link each theory or discovery to its principal proponent.

 

Question 41. Some so called doctors claim that their medicines provide 100% guarantee for getting a son or a daughter according to the wish of the parent. How do you react to such claims on the basis of your knowledge of genetics? Give a suitable explanation.
Answer: Such claims are incorrect. The sex of a fetus is determined by the sex chromosomes. Human females are homogametic, producing only one type of egg (X chromosome), while males are heterogametic, producing two types of sperm (X-carrying and Y-carrying). The sex of the offspring depends on whether an X-carrying sperm or a Y-carrying sperm fertilizes the egg.
In simple words: Claims of guaranteeing a baby's sex with medicine are false because a baby's sex is naturally determined by the father's sperm, which carries either an X or Y chromosome, not by external interventions.

🎯 Exam Tip: Clearly explain the chromosomal basis of sex determination in humans, emphasizing the role of the father's sperm in contributing either an X or Y chromosome, to debunk pseudoscientific claims.

 

Question 42. What will be the sex of a child which develops from 44 + XX zygote?
Answer: Female
In simple words: A zygote with 44 autosomes and two X chromosomes (XX) will develop into a female.

🎯 Exam Tip: Remember that in humans, the presence of two X chromosomes (XX) leads to female development, while an X and a Y chromosome (XY) lead to male development.

 

Question 43. What is haemophilia due to? What happens in this disorder?
Answer: Haemophilia is caused by a defective recessive allele located on the X chromosome. This disorder affects a specific protein crucial for blood clotting. As a result, individuals with haemophilia experience excessive bleeding even from minor cuts, which can be life-threatening.
In simple words: Haemophilia is a genetic disorder caused by a faulty gene on the X chromosome that prevents blood from clotting properly, making even small injuries dangerous due to continuous bleeding.

🎯 Exam Tip: When describing haemophilia, highlight its X-linked recessive inheritance pattern and the consequence of impaired blood clotting due to a missing or defective protein.

 

Question 44. Drosophila is known as the 'pea' of animal kingdom. Justify this statement.
Answer: Drosophila, the fruit fly, is considered the 'pea' of the animal kingdom because it serves as an ideal model organism for genetic studies, much like the garden pea (Pisum sativum) in the plant kingdom. This is due to its rapid reproduction, short life cycle, ease of breeding, production of numerous offspring, and easily observable traits.
In simple words: Drosophila is called the 'pea' of the animal kingdom because, like Mendel's pea plants, it's perfect for genetic studies due to its quick reproduction, short life cycle, and easy-to-observe genetic traits.

🎯 Exam Tip: Justify why a model organism is ideal for genetic research by listing its advantageous characteristics such as short generation time, large progeny, and observable traits.

 

Question 45. Some genetic disorders such as haemophilia, colour blindness etc. transmit from father to grandson through daughter. Name the type of inheritance.
Answer: Criss-cross inheritance (or) zig-zag inheritance
In simple words: When a trait skips a generation and passes from a grandfather to his grandson through an unaffected daughter, it's called criss-cross inheritance.

🎯 Exam Tip: Recognize criss-cross inheritance as a characteristic pattern for X-linked recessive disorders, where the trait appears in males, is transmitted by carrier females, and affects their sons.

 

Question 46. Give one word for the following.
a. Agents that cause mutation.
b. Diagrammatic representation of karyotype
c. Seat of genes
d. Loss of chromosome segment
e. Fixed position of a gene
f. Exchange of segments between non-sister chromatids
g. Failure of separation of chromosome during meiosis.
h. A chromosome pair is lost from the diploid set.
Answer:
(a) Mutagens
(b) Idiogram
(c) Chromosome
(d) Deletion
(e) Locus
(f) Crossing over
(g) Non-disjunction
(h) Nullisomic
In simple words: This question asks for single terms to define various genetic processes, structures, and abnormalities.

🎯 Exam Tip: A strong vocabulary of genetic terms is crucial. Ensure you can accurately define concepts related to mutations, chromosome structure, gene location, and chromosomal abnormalities.

 

Question 47. Match the related items from B and C with column A.
Answer:

A	B	C
i. Turner's syndrome	c. 44A + X	i. Sterile female
ii. Sickle cell anemia	d. Substitution of wrong aminoacid	h. Abnormal Hb
iii. Klinefelter's syndrome	e. 44A + XXY	f. Sterile male
iv. Phenylketonuria	b. Inborn error of metabolism	j. Lack of phenyl alanine hydroxylase
v. Cystic fibrosis	a. Autosomal defect (Chromosome No.7)	g. Failure of chloride ion transport

In simple words: This matching exercise connects genetic disorders with their specific chromosomal causes, molecular defects, and resulting symptoms or characteristics.

🎯 Exam Tip: For matching questions on genetic disorders, focus on linking the disorder name to its primary genetic cause (e.g., chromosomal abnormality, gene mutation) and its most characteristic symptom.

 

Question 48. Give the chromosome numbers of the following animals and plants.
Answer:

Animals	Plants
i. Ascaris megalocephala - 2	a. Pisum sativum - 14
ii. Drosophila melanogaster - 8	b. Allium cepa - 16
iii. Apis (honey bee) - 32	c. Oryza sativa - 24
iv. Homosapiens - 46	d. Ophioglossum reticulatum - 1262
v. Equus (horse) - 64	e. Saccharum officinarum - 80
vi. Culex - 6	f. Solanum tuberosum - 48

In simple words: This table provides the chromosome numbers for various animals and plants, highlighting the diversity in genetic composition across different species.

🎯 Exam Tip: While memorizing all chromosome numbers might be challenging, focusing on commonly studied organisms in genetics (like humans, Drosophila, pea plants) is beneficial.

 

Question 49. Complete the flow chart.
Answer: In many insects and roundworms, females possess two 'X' chromosomes (XX), while males have only one 'X' chromosome (XO), meaning the male has one chromosome fewer than the female. For example, in grasshoppers, females have 22 autosomes and two X chromosomes (XX), whereas males have 22 autosomes and only one X chromosome (XO). The female produces only one type of egg, carrying an X chromosome. The male, however, produces two types of sperm: one carrying 11 autosomes and an X chromosome (11A + X), and the other carrying 11 autosomes only (11A + O). Fertilization of an X-carrying egg by an X-sperm produces a female (XX), while fertilization by an O-sperm produces a male (XO).

ℹ️ चित्र व्याख्या (Diagram Explanation): यह फ्लोचार्ट XO प्रकार के लिंग निर्धारण को दर्शाता है, जहाँ एक पिता (22A + XO) और एक माता (22A + XX) के बीच क्रॉस होता है. पिता दो प्रकार के युग्मक (11A + X, 11A + O) उत्पन्न करता है, जबकि माता केवल एक प्रकार का युग्मक (11A + X) उत्पन्न करती है. यह दर्शाता है कि संतानों में लिंग का निर्धारण कैसे होता है, जिससे मादा (22A + XX) और नर (22A + XO) संतति प्राप्त होती है.

Parents	Father 22A + XO	x	Mother 22A + XX
Gametes	11A + X 11A + O		11A + X
F1	22A + XX Female		22A + XO Male

In simple words: This flowchart explains XO sex determination, where males have one less sex chromosome (XO) than females (XX). The father determines sex by producing two types of sperm (X or O), while the mother produces only X eggs.

🎯 Exam Tip: When completing flowcharts for sex determination, ensure you correctly show the gametes produced by each parent and how their fusion leads to the specific sex of the offspring, according to the given mechanism (e.g., XO type).

 

Question 50. Correct the amino acid sequence of sickle cell haemoglobin.
Answer: The correct amino acid sequence for normal hemoglobin in this specific segment is Val - His - Leu - Thr - Pro - Glu. In sickle cell hemoglobin, the correct sequence is Val - His - Leu - Thr - Pro - Val, where Glutamic acid (Glu) is replaced by Valine (Val).
In simple words: In normal hemoglobin, the amino acid sequence includes Glutamic acid at a key position, but in sickle cell hemoglobin, this is incorrectly replaced by Valine.

🎯 Exam Tip: Know the specific amino acid substitution in sickle cell anemia (glutamic acid to valine at the 6th position of the beta-globin chain) as it's a fundamental example of a point mutation.

 

Question 51. Down's syndrome may occur in both sexes. Comment.
Answer: Down's syndrome is an autosomal abnormality, characterized by the presence of an extra copy of chromosome 21 (trisomy 21). Since chromosome 21 is an autosome (non-sex chromosome), this condition affects both males and females equally, regardless of their sex chromosomes.
In simple words: Down's syndrome affects males and females because it's caused by an extra copy of chromosome 21, which is not a sex chromosome.

🎯 Exam Tip: When discussing Down's syndrome, emphasize that it is an autosomal trisomy, meaning it's a condition related to non-sex chromosomes, hence its occurrence is independent of sex.

 

Question 52. Sets of four individuals are given below 45A + XXY, 45A + XO, 45A + XX, 45A + XY.
a. How many body chromosomes and sex chromosomes are present in normal males and females?
b. Identify and write the names of chromosomal abnormalities in the above-listed chromosome sets.
c. Down's syndrome is seen in both sexes. Comment.
Answer:
(a) In normal human males, there are 22 pairs of autosomes (body chromosomes) and one pair of allosomes (sex chromosomes), totaling 46 chromosomes (44A + XY). In normal human females, there are 22 pairs of autosomes and one pair of allosomes, totaling 46 chromosomes (44A + XX).
(b) From the listed chromosome sets:
- 45A + XXY: Klinefelter's syndrome (male)
- 45A + XO: Turner's syndrome (female)
- 45A + XX: Down's syndrome (female)
- 45A + XY: Down's syndrome (male)
(c) Down's syndrome is a trisomy of the 21st chromosome, meaning there is an extra copy of chromosome 21. Since chromosome 21 is an autosome (not a sex chromosome), this abnormality affects individuals regardless of their sex, and therefore can be observed in both males and females.
In simple words: Normal humans have 22 pairs of body chromosomes and one pair of sex chromosomes. The listed sets show chromosomal abnormalities like Klinefelter's (XXY), Turner's (XO), and Down's syndrome (extra chromosome 21), which can occur in both sexes because it involves a non-sex chromosome.

🎯 Exam Tip: Clearly distinguish between autosomal and sex chromosome abnormalities. For each syndrome, know the specific chromosomal deviation and its phenotypic sex determination.

 

Question 1. Mendel's which law of inheritance is universally accepted without any exception? State the law.
Answer: Mendel's first law, the Law of Dominance, is not universally accepted without exception, as phenomena like incomplete dominance and co-dominance are exceptions. The Law of Segregation, however, is universally accepted without known exceptions. It states that during gamete formation, the two alleles for a heritable character separate (segregate) from each other such that each gamete receives only one allele.
In simple words: Mendel's Law of Segregation is universally accepted; it states that during reproduction, each parent passes only one of their two gene copies for a trait to their offspring.

🎯 Exam Tip: Remember that while the Law of Dominance has exceptions (like incomplete dominance), the Law of Segregation is a fundamental principle of genetics with no known exceptions.

 

Question 2. AaBb was crossed with aabb. What would be the phenotypic ratio of the progeny? Mention the term to denote this kind of cross.
Answer: The phenotypic ratio of the progeny resulting from a cross between AaBb and aabb is 1:1:1:1. This type of cross is known as a dihybrid test cross, where a heterozygous individual for two traits is crossed with an individual homozygous recessive for both traits.
In simple words: When crossing AaBb with aabb, the offspring will show a 1:1:1:1 ratio of phenotypes. This specific cross is called a dihybrid test cross.

🎯 Exam Tip: A 1:1:1:1 phenotypic ratio in a dihybrid cross is a classic indicator of a dihybrid test cross, where the unknown parent is heterozygous for both traits.

 

Question 3. The table shows the genotypes for ABO blood grouping and their phenotypes. Complete the left in the table.
Answer:

Sl.No.	Genotype	Blood group
i.	IAIA	A
ii.	IAIO	A
iii.	IBIB	B
iv.	IBIO	B
v.	IAIB	AB
vi.	IOIO	O

In simple words: This table maps the various genetic combinations (genotypes) for the ABO blood group system to their corresponding observable blood types (phenotypes).

🎯 Exam Tip: Understand that ABO blood grouping demonstrates multiple alleles and co-dominance. Memorize the specific genotypes for each blood phenotype (A, B, AB, O).

 

Question 4. Describe sex determination in certain Birds.
Answer:In avian species, sex determination follows the ZW system, where both male and female individuals possess an identical number of chromosomes. Males typically carry autosomes along with two Z-chromosomes (ZZ). Females, however, have autosomes and one Z and one W-chromosome (ZW). Males are homogametic, producing only one type of sperm, each containing a Z-chromosome and autosomes. Conversely, females are heterogametic, generating two types of ova: 50% carry a Z-chromosome, and the other 50% carry a W-chromosome. The sex of the progeny is thus determined by the specific type of ovum that undergoes fertilization. If an ovum with a Z-chromosome is fertilized, the resulting zygote (ZZ) develops into a male. If an ovum with a W-chromosome is fertilized, the zygote (ZW) develops into a female.
In simple words: Birds have a ZW sex determination system. Males are ZZ, and females are ZW. The female determines the sex of the offspring through the type of egg (Z or W) that is fertilized by the male's Z sperm.

🎯 Exam Tip: Understanding the ZW system's contrast with the XY system (found in humans) is crucial for questions on genetic inheritance patterns.