1. What is a gene?
Answer. Gene is the unit of inheritance. Gene is the part of a chromosome which controls the
appearance of a set of hereditary characteristics.

2. What is a sex chromosome?
 Answer. Sex chromosome is a chromosome that operates in the sex-determining mechanism of a species. Many animals have two different types of sex chromosomes. For example, in human there is a large X chromosome and a much smaller Y chromosome.

3. “The sex of the children is determined by what they inherit from their father and not their
mother.” Justify.
Answer. It is because a child who inherits an X chromosome from her father will be a girl and
one who inherits a Y chromosome from his father will be a boy. But all children inherit a X
chromosome from their mother regardless of whether they are boys or girls.

4. Define variation in relation to a species. Why is variation beneficial to the species?
Answer. Variation refers to the differences in the characters or traits among the individuals of a
species. Variations are beneficial to the species because:
a) They enable the organisms to adapt themselves in changing environment.
b) Variations form the basis of heredity.
c) They form the raw materials for evolution and development of new species.

5. Distinguish between acquired and inherited traits by giving one example of each. Why are
traits acquired during the lifetime of an individual not inherited?
Answer. Acquired trait is a particular characteristic that is developed during the lifetime of an
individual. Such characteristics are not genetically controlled and cannot be passed on to the next
generation. Example: Loss of weight due to starvation.
Inherited trait is the transmission of particular characteristics from parents to their off springs,
generation to generation. Such traits are genetically determined characteristic that distinguishes a

Example: Colour of skin.
The acquired traits cannot change the DNA of the germ cells. Therefore, the acquired traits cannot
be inherited over generations during the lifetime of an individual.

6. The human beings who look so different from each other in terms of colour, size and looks
are said to belong to the same species. Why? Justify your answer.
Answer. Human beings are said to belong to the same species because of the following reasons:
DNA studies. Number of chromosome is same, All have a common ancestor.
They interbreed among themselves to produce fertile young ones of their own kind.

7. Explain the mechanism of sex determination in humans.
With the help of a flow chart explain in brief how the sex of a newborn is genetically
determined in human beings. Which of the two parents, the mother or the father, is
responsible for determination of sex of a child?
Answer. Mechanism of Sex Determination in Human Beings:
In human beings, the sex of the individual is genetically determined.
  •  Sex determination is the process by which sex of a new born individual can be determined.
  •  Human beings have 1 unpaired sex chromosome. Sex chromosome of male is XY and of female is XX.
  •  Sex of a child depends on what happens at fertilization

Thus, father is responsible for the determination of the sex of a child.

8. Give one example each of characters that are inherited and the ones that are acquired in
humans. Mention the difference between the inherited and the acquired characters. 
Answer. Eye colour or hair colour of a person is an example of inherited character whereas, body weight is an example of acquired character.
The basic difference between inherited and acquired character is that inherited character is passed
on from parent to offspring and acquired characters are acquired by an individual during his
lifetime depending upon his lifestyle. 

9. How is the equal genetic contribution of male and female parents ensured in the progeny?
Answer. During sexual reproduction, a female gamete or egg cell fuses with a male gamete or
sperm cell which are haploid to form zygote. Zygote is diploid which contains 23 chromosomes
from mother and 23 from father. In this way, an equal genetic contribution of male and female
parents is ensured in the progeny

10. A blue colour flower plant denoted by BB is cross bred with that of white colour flower
plant denoted by bb.
(a) State the colour of flower you would expect in their F1 generation plants.
(b) What must be the percentage of white flower plants in F2 generation if flowers
of F1 plants are self-pollinated?
(c) State the expected ratio of the genotypes BB and Bb in the F2 progeny. [Delhi]

11. State the meaning of inherited traits and acquired traits. Which of the two is not passed on
to the next generation? Explain with the help of an example.
Answer. Inherited traits are the characteristics transmitted from parents to their
offspring. Acquired traits are characteristics which are developed during the lifetime of an
individual. Acquired traits are not passed on to the next generation. For example, if we breed a
group of mice, all their progeny will have tails. Now, if the tails of these mice are removed by
surgery and allowed to breed, the next generation mice will also have tails. If these tails are also
removed and allowed to breed, the progeny of mice will again have tails. Removal of tail by
surgery is an acquired trait and do not change the genes of germ cells and hence, are not passed
on to the next generation.

12. “An individual cannot pass on to its progeny the experiences of its lifetime.” Justify the
statement with the help of an example and also give reason for the same.
Answer. Experience achieved during the lifetime of an individual does not make any change in
the gene of the individual.
For example, if a person reads a book on birds, the knowledge he earns by reading the book does
not make any change in the gene, hence, this knowledge will not get automatically transmitted to
his next generation. Such a trait is called acquired trait.

13. How do Mendel’s experiments show that the (a) traits may be dominant or recessive, (b)
traits are inherited independently?
Answer. Mendel’s Experiments on Inheritance of Traits. Mendel used a number of visible
contrasting characters of garden pea like round/wrinkled seeds, tall/short plants, white/violet
flowers, etc.

Two Visible Contrasting Characters:
• Mendel took pea plants with two different characteristics such as plant with round and green
seed and plant with wrinkled and yellow seeds and cross-pollinated then to get F1 progeny.
• In F1 progeny, all the plants will have round and yellow seeds. The round and yellow are
dominant traits.
• Mendel then allowed F1 progeny plants for self-pollination to get F2 progeny.
• F2 progeny will have plants with round and yellow seeds, round and green seeds, wrinkled and
yellow seeds, wrinkled and green seed.
• The ratio of plants with above characteristics will be 9 : 3 : 3 : 1
• Therefore, round seed/wrinkled seed trait are independently inherited.

(a) In F1 progeny, all the plants will have round and yellow seeds. Wrinkled and green traits were
not seen. But wrinkled and green characters appeared in the F2 progeny.
This means that wrinkle and green characters were recessive trait in F1 progeny, whereas round
and yellow traits were dominant trait.
(b) New mixture of traits are seen in both F1 and F2 progeny. This means traits are independently


1. Exchange of genetic material takes place in
(a) vegetative reproduction 
(b) asexual reproduction
(c) sexual reproduction 
(d) budding

2. Two pink coloured flowers on crossing resulted in 1 red, 2 pink and 1 white flower progeny. The nature of the cross will be
(a) double fertilization 
(b) self pollination
(c) cross fertilization 
(d) no fertilisation

3. A cross between a tall plant (TT) and short pea plant (tt) resulted in progeny that were all tall
plants because
(a) tallness is the dominant trait
(b) shortness is the dominant trait
(c) tallness is the recessive trait
(d) height of pea plant is not governed by gene ‘T’ or ‘t’

4. Which of the following statement is incorrect?
(a) For every hormone there is a gene.
(b) For every protein there is a gene.
(c) For production of every enzyme there is a gene.
(d) For every molecule of fat there is a gene

5. If a round, green seeded pea plant (RR yy) is crossed with wrinkled, yellow seeded pea plant, (rr
YY) the seeds produced in F1 generation are
(a) round and yellow
(b) round and green
(c) wrinkled and green
(d) wrinkled and yellow

6. In human males all the chromosomes are paired perfectly except one. This/these unpaired
chromosome is/are
(i) large chromosome
(ii) small chromosome
(iii) Y-chromosome
(iv) X-chromosome
(a) (i) and (ii) 
(b) (iii) only
(c) (iii) and (iv) 
(d) (ii) and (iv)

7. The maleness of a child is determined by
(a) the X chromosome in the zygote
(b) the Y chromosome in zygote
(c) the cytoplasm of germ cell which determines the sex
(d) sex is determined by chance

8. A zygote which has an X-chromosome inherited from the father will develop into a
(a) boy
(b) girl
(c) X- chromosome does not determine the sex of a child
(d) either boy or girl

9. Select the incorrect statement
(a) Frequency of certain genes in a population change over several generations resulting in
(b) Reduction in weight of the organism due to starvation is genetically controlled
(c) Low weight parents can have heavy weight progeny
(d) Traits which are not inherited over generations do not cause evolution

10. New species may be formed if
(i) DNA undergoes significant changes in germ cells
(ii) chromosome number changes in the gamete
(iii) there is no change in the genetic material
(iv) mating does not take place
(a) (i) and (ii) 
(b) (i) and (iii)
(c) (ii), (iii) and (iv) 
(d) (i), (ii) and (iii)

11. Two pea plants one with round green seeds (RRyy) and another with wrinkled yellow (rrYY)
seeds produce F1 progeny that have round, yellow (RrYy) seeds. When F1 plants are selfed, the
F2 progeny will have new combination of characters. Choose the new combination from the
(i) Round, yellow
(ii) Round, green
(iii) Wrinkled, yellow
(iv) Wrinkled, green
(a) (i) and (ii) 
(b) (i) and (iv)
(c) (ii) and (iii) 
(d) (i) and (iii)

12. A basket of vegetables contains carrot, potato, radish and tomato. Which of them represent the correct homologous structures?
(a) Carrot and potato
(b) Carrot and tomato
(c) Radish and carrot
(d) Radish and potato

13. Select the correct statement
(a) Tendril of a pea plant and phylloclade of Opuntia are homologous
(b) Tendril of a pea plant and phylloclade of Opuntia are analogous
(c) Wings of birds and limbs of lizards are analogous
(d) Wings of birds and wings of bat are homologous

14. Which of the following statements is not true with respect to variation?
(a) All variations in a species have equal chance of survival
(b) Change in genetic composition results in variation
(c) Selection of variants by environmental factors forms the basis of evolutionary processes.
(d) Variation is minimum in asexual reproduction

15. A trait in an organism is influenced by
(a) paternal DNA only
(b) maternal DNA only
(c) both maternal and paternal DNA
(d) neither by paternal nor by maternal DNA

16. Select the group which shares maximum number of common characters
(a) two individuals of a species
(b) two species of a genus
(c) two genera of a family
(d) two genera of two families

17. The number of pair (s) of sex chromosomes in the zygote of humans is
(a) one 
(b) two 
(c) three 
(d) four

18. In peas, a pure tall plant (TT) is crossed with a short plant (tt). The ratio of pure tall plants to short plants in F2 is
(a) 1 : 3 
(b) 3 : 1 
(c) 1 : 1 
(d) 2 : 1

19. From the list given below, select the character which can be acquired but not inherited
(a) colour of eye
(b) colour of skin
(c) size of body
(d) nature of hair

20. The two versions of a trait (character) which are brought in by the male and female gametes are situated on
(a) copies of the same chromosome
(b) two different chromosomes
(c) sex chromosomes
(d) any chromosome

21. Select the statements that describe characteristics of genes
(i) genes are specific sequence of bases in a DNA molecule
(ii) a gene does not code for proteins
(iii) in individuals of a given species, a specific gene is located on a particular chromosome
(iv) each chromosome has only one gene

(a) (i) and (ii) 
(b) (i) and (iii)
(c) (i) and (iv) 
(d) (ii) and (iv)