CBSE Class 10 Biology Heredity Worksheet Set G

Very Short Answer Type Questions :

Question. A Mendelian experiment consisted of breeding pea plants bearing violet flowers with pea plants bearing white flowers. What will be the result in F1 progeny?
Answer: Violet flowers.

Question. What is heredity?
Answer: The transmission of characteristics from one generation to another is known as heredity.

Question. Mendel took tall pea plants and short pea plants and produced F1 progeny through crossfertilisation What did Mendel observe in the F1 progeny?
Answer: All pea plant were tall in F1 generation.

Question. How many pairs of chromosomes are present in human beings? 
Answer: 23 pairs.

Question. What is DNA?
Answer: DNA is the carrier of hereditary information from parents to the next generation.

Question. What is a gene?
Answer: Gene is a part of DNA that encodes the instructions that allow a cell to produce a specific protein or enzyme.

Question. Where is DNA found in a cell?
Answer: DNA is found in the cell nucleus.

 Question. Name the information source for making proteins in the cells. 
Answer: Cellular DNA is the information source for making proteins in cells.

Short Answer Type Questions :

Question. Give the respective scientific terms used for studying:
(i) The mechanism by which variations are created and inherited and
(ii) The development of new type of organisms form from the existing ones.
Answer: (i) Genetics is the study of mechanism by which variations are created and inherited.
(ii) Evolution is used for studying the development of new type of organisms from the existing ones.

Question. ‘Gene control traits’? Explain this statement with an example. 
Answer: Gene controls the trait by synthesizing the specific enzyme. Consider tallness as a trait. Plant height depends upon particular plant hormone which in turn will depend on the efficiency of the process for making it. If the enzyme responsible for the production of this hormone is efficient, plant will be tall. If the gene for that enzyme has an alteration that makes enzyme less efficient, the amount of hormone will be less and plant will be short.

Question. Name the plant Mendel used for his experiment.
What type of progeny was obtained by Mendel in F1 and F2 generations when he crossed the tall and short plants? Write the ratio he obtained in F2 generation plants.
Answer: Pea Plant / Garden pea / Pisum sativum
F1 – All tall; F2- Tall and short
Ratio – Tall: Short
3: 1 / 1: 2: 1

Question. What is DNA copying? State its importance.
Answer: DNA replication or DNA copying is the process of producing two identical replicas from one original DNA molecule during cell division.
Importance of DNA Copying:
(i) DNA replication needs to occur so that during cell division, new cells will also have a copy of organism’s DNA.
(ii) DNA is necessary to make all the RNA and proteins needed for cells to carry out necessary reactions and cellular processes in order to survive.

Question. How do Mendel’s experiment show that traits are inherited independently?
Answer: (i) When a cross was made between a tall pea plant with round seeds and a short pea plant with wrinkled seeds, the F1 progeny plants are all tall with round seeds. This indicates that tallness and round seeds are the dominant traits.
(ii) When the F1 plants are self-pollinated, the F2 progeny consist of some tall plants with round seeds and some short plants with wrinkled seeds which are the parental traits. 
(iii) There were also some new combinations like tall plants with wrinkled seeds and short plants with round seeds. 
(iv) Thus, it may be concluded that tall and short traits and round and wrinkled seed traits have been inherited independently.
OR
A flow chart depicting the same.
Note: Any other contrasting characters can also be taken

Question. If we cross-bred tall (dominant) pea plant with pure-bred dwarf (recessive) pea plant, we will get plants of F1 generation. If we now self-cross the pea plant of F1 generation, we obtain pea plants of F2 generation.
(i) What do the plants of F1 generation look like?
(ii) State the ratio of tall plant to dwarf plants in F2 generation.
(iii) State the type of plants not found in F1 generation but appeared in F2 generation. Write the reason for the same. 
Answer: (i) Tall 
(ii) 3: 1 
(iii) Dwarf 
Reason: Being a recessive trait, dwarfness can only be expressed in the recessive homozygous condition or in the absence of dominant trait.

Question. “The chromosome number of the sexually reproducing parents and their offspring is the same.” Justify this statement. 
Answer: Male individual have 46 chromosomes but because the gametes are always haploid i.e., they have half the number of chromosomes; sperms will be haploid (23 chromosomes). Female individual also contains only 23 chromosomes in egg. It is the fusion of the sperm and egg which leads to an offsprings with 46 chromosomes.

Question. In humans, there is a 50% probability of the birth of a boy and 50 % probability that a girl will be born. Justify the statement on the basis of the mechanism of sex-determination in human beings.
Answer: In human beings, the genes inherited from our parents decide whether it will be a boy or girl.
Women have a perfect pair of sex chromosomes (XX). But, men have a mismatched pair (XY).
All children will inherit an X chromosome from their mother regardless of whether they are boys or girls. Thus, the sex of the children will be determined by what they inherit from their father.
A child who inherits an X chromosome from her father will be a girl, and one who inherits a Y chromosome from him will be a boy.

Question. After self-pollination in pea plants with round, yellow seeds, following types of seeds were obtained by Mendel:
Analyse the result and describe the mechanism of inheritance which explains these results.
Answer: The ratio obtained is 9:3:3:1 in which parental as well as new combinations are observed. This indicates that progeny plants have not inherited the whole set of genes from each parent. Every germ cell takes on chromosome from the pair of maternal and paternal chromosomes.
When two germ cells combine, segregation of one pair of characters is independent of other pair of characters.

Question. How did Mendel interpret his result to show that traits may be dominant or recessive? Describe briefly.
Answer: Mendel conducted breeding experiments on Pea plants.
(i) He selected pure breed tall and dwarf plants. 
(ii) He cross-pollinated these plants. 
(iii) In the F1 generation, he obtained only tall plants.
Tallness is the dominant trait. 
(iv) Then, he produced F2 generation by self cross of hybrids / F1. 
(v) He found that 3/4th of the plants were tall and 1/4th were dwarf. 
(vi) The trait which remains hidden in F1 generation plants is the recessive traits.

Question. ‘Different species use different strategies to determine sex of a newborn individual. It can be environmental cues or genetically determined.’
Explain the statement by giving example for each strategy. 
Answer: Environmental Cue: (i) In some animals, the temperature at which fertilised eggs are kept determines whether the developing animal in egg is male or female.
(ii) In some animals like snail, individual can change sex.
Genetical Cue: A child who inherits an X-chromosome from her father will be a girl and one who inherits a Y- chromosome from the father will be a boy.

 Question. How do Mendel’s experiments show that (a) Traits may be dominant or recessive?
(b) Inheritance of two traits is independent of each other? 
Answer: (a) Mendel conducted a Monohybrid cross/ (crossed pure tall pea plants with pure dwarf pea plants) he observed only tall pea plants in the F1 generation, but on self crossing of the F1 progeny, both tall and dwarf pea plants were observed in F2 generation in the ratio 3: 1. Appearance of tall character in F1 and F2 generations shows tallness to be a dominant character. But absence of dwarf character in F1 and its reappearance in F2 confirms that dwarfness is recessive character. 
(b) Mendel conducted a dihybrid cross and observed that though he started with two types of parents, he obtained four types of individuals in F2.
The appearance of new recombination in F2 generations along with parental type characters showed that traits are inherited independently of each other.

Question. Differentiate between dominant and recessive traits.
Answer: (a) The character which gets expressed in the presence of its contrasting form is termed as dominant trait.
(b) The trait which remains unexpressed in the presence of its contrasting form is called recessive trait.

Question. In a monohybrid cross between tall pea plants (TT) and short pea plants (tt) a scientist obtained only tall pea plants (Tt) in the F1 generation.
However, on self cross of the F1 generation pea plants, he obtained both tall and short plants in F2 generation. On the basis of above observations with other angiosperms also, can the scientist arrive at a law? If yes, explain the law. If not, give justification for your answer.
Answer: Yes, the scientist may arrive at the law of dominance according to which the trait that is expressed in the F1 generation is the dominant trait, although both the dominant and recessive traits are present in the F1 generation. In the F2 generation the recessive traits is also expressed along with the dominant traits.

Long Answer Type Questions :

Question. (a) Why did Mendel choose garden pea for his experiments? Write two reasons.
(b) List two contrasting visible characters of garden pea Mendel used for his experiment.
(c) Explain in brief how Mendel interpreted his results to show that the traits may be dominant or recessive.
Answer: (a) Reasons:
(i) Pea plant is small and easy to grow.
(ii) A large number of true breeding varieties of pea plant are available.
(iii) Short life cycle. (iv) Both self and cross-pollination can be made possible. (Any two reasons)
(b) Contrasting characters:
Round / Wrinkled seeds
Tall / Short plants
White / Purple flowers
Green / Yellow seeds (Or any other)
(c) When Mendel crossed two pea plants with a pair of contrasting characters, only one character appeared in all the members of F1 progeny and the others remain hidden.
On selfing F1, the hidden characters reappeared in just 25% of the offsprings and the other 75% shared the characters expressed in F1.
Mendel concluded that the character which expresses itself in F1 and in 75% of the individuals of F2 is dominating while the other is recessive.

Question. (a) What is variation? How is variation created in a population? How does the creation of variation in a species promote survival?
(b) Explain how, offspring and parents of organisms reproducing sexually have the same number of chromosomes. 
Answer: (a) Occurrence of differences between organisms is called variation.
New variation may arise during the process of DNA copying that already has variations accumulated from previous generations.
Combining variations from two or more individuals would thus create new combinations of variations.
Species having suitable variations have more chances of survival in case of change in environment conditions.
(b) In sexually reproducing organisms, male and female gametes/reproductive cells with only half the number of chromosomes (as in the parent cell) are produced. During fertilization, when male and female gametes fuse to give rise to a zygote, original number of chromosomes are restored.