Chapter 8: Heredity and Evolution

Multiple Choice Questions

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

Answer: (c) Sexual reproduction.

[Genetic material exchange occurs during the formation of gametes (sperm and egg), leading to genetic diversity in offspring. This process enhances adaptability and evolution within a population.]

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 fertilisation
(b) self pollination
(c) cross fertilisation
(d) no fertilisation

Answer: (b) self-pollination.

[ The consistent appearance of pink flowers indicates a stable trait, and the presence of red and white flowers suggests a genetic combination resulting from self-pollination.]

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’
Answer: (a) Tallness is the dominant trait.

[In this case, the dominant allele (T) from the tall parent masks the expression of the recessive allele (t) from the short parent, resulting in all tall progeny.]

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

Answer : (d) For every molecule of fat, there is a gene.

[ This statement is incorrect. The synthesis of molecules like fats is not directly controlled by individual genes; it involves complex interactions and multiple genes, not a one-to-one relationship.]

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
Answer : (a) Round and yellow.

[ The uppercase letters represent dominant alleles, and the lowercase letters represent recessive alleles. In this cross, the F1 generation will be heterozygous for both traits (Rr Yy), resulting in round (dominant) and yellow (dominant) seeds.]

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)

Answer : (c) (iii) Y-chromosome and (iv) X-chromosome.

[ In human males, the sex chromosomes are not perfectly paired; they consist of one X-chromosome and one Y-chromosome.]

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

Answer : (b) The Y chromosome in the zygote.

[ The presence of a Y chromosome in the fertilized egg determines maleness, while the absence of a Y chromosome results in femaleness.]

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

Answer : (b) Girl.

[ In humans, females have two X chromosomes (XX), and if a zygote inherits an X chromosome from the father, it will develop into a girl. ]

9. Select the incorrect statement
(a) Frequency of certain genes in a population change over several generations resulting in evolution
(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

Answer: (b) Reduction in weight of the organism due to starvation is genetically controlled.

[ This statement is incorrect. Weight reduction due to starvation is primarily influenced by environmental factors and not solely controlled by genetics.]

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)

Answer : (a) (i) and (ii).

[ New species may be formed if DNA undergoes significant changes in germ cells (genetic mutations) and if there are changes in chromosome number in the gametes (e.g., through chromosomal rearrangements or errors in meiosis). ]

11. Two pea plants one with round green seeds (RRyy) and another with wrinkled yellow (rrYY) seeds produce progeny that have round, yellow (RrYy) seeds. When plants are selfed, the
progeny will have new combination of characters. Choose the new combination from the following
(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)

Answer: (b) (i) and (iv).

[ The progeny can have new combinations of characters, including round green (RrYy) and wrinkled yellow (rrYy). ]

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

Answer: (c) Radish and carrot.

[ Both are modified roots performing similar functions, showing same basic structure and origin, hence they are homologous structures.]

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

Answer : (a) Tendril of a pea plant and phylloclade of Opuntia are homologous.

[ They both represent modified plant structures derived from the same ancestral form. ]

14. If the fossil of an organism is found in the deeper layers of earth, then we can predict that
(a) the extinction of organism has occurred recently
(b) the extinction of organism has occurred thousands of years ago
(c) the fossil position in the layers of earth is not related to its time of extinction
(d) time of extinction cannot be determined

Answer:  (b) the extinction of organism has occurred thousands of years ago.

[ Deeper layers of earth are older. So fossils found there belong to organisms that lived long ago and got extinct earlier than those found in upper layers.]

15. 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

Answer: (a) All variations in a species have an equal chance of survival.

[ This statement is not true. Natural selection acts on variations, and not all variations have an equal chance of survival; the ones that provide a better adaptation to the environment are more likely to survive and reproduce.]

16. 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

Answer: (c) Both maternal and paternal DNA.

[ Traits in an organism are influenced by the combination of genetic material inherited from both the mother and the father, contributing to the organism's overall genetic makeup.]

17. 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

Answer : (a) Two individuals of a species.

[ Individuals within the same species share the maximum number of common characters because they belong to the same biological species and have a common gene pool. ]

18. According to the evolutionary theory, formation of a new species is generally due to
(a) sudden creation by nature
(b) accumulation of variations over several generations
(c) clones formed during asexual reproduction
(d) movement of individuals from one habitat to another

Answer: (b) accumulation of variations over several generations

[ New species are formed when small variations keep accumulating in a population over many generations, leading to reproductive isolation and eventually formation of a new species.]

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

Answer : (c) Size of body.

[ The size of the body can be influenced by various environmental factors such as nutrition and health during an individual's lifetime, but it is not directly inherited through genetic material.]

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

Answer: (a) Copies of the same chromosome.

[ The two versions of a trait, one from each parent, are typically located on homologous chromosomes, which are pairs of chromosomes that carry the same genes at corresponding loci. ]

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)

Answer:  (b) (i) and (iii).

[ Genes are specific sequences of bases in a DNA molecule, and in individuals of a given species, a specific gene is located on a particular chromosome. The other statements are not accurate; genes generally code for proteins, and each chromosome can have multiple genes.]

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

Answer:  (b) 3 : 1.

[ In the given cross, Tt (heterozygous tall) is formed in the generation, and when these individuals are self-pollinated, the genotype ratio in the generation is 1 TT : 2 Tt : 1 tt, resulting in a phenotypic ratio of 3 tall : 1 short.]

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

Answer:  (a) One.

[ Humans have one pair of sex chromosomes in the zygote. Males have XY, and females have XX, making one pair of sex chromosomes in total.]

24. The theory of evolution of species by natural selection was given by
(a) Mendel         (b) Darwin         (c) Morgan         (d) Lamarck

Answer: (b) Darwin

[ Charles Darwin proposed the theory of evolution of species by natural selection.]

25. Some dinosaurs had feathers although they could not fly but birds have feathers that help them to fly. In the context of evolution this means that
(a) reptiles have evolved from birds
(b) there is no evolutionary connection between reptiles and birds
(c) feathers are homologous structures in both the organisms
(d) birds have evolved from reptiles

Answer: (d) birds have evolved from reptiles

[ Feathered dinosaurs show a transitional stage, indicating that birds evolved from reptilian ancestors over time through evolutionary changes.]

Short Answer Questions

21. How is the sex of a newborn determined in humans?

Answer: In humans, the mother always gives an X chromosome, while the father gives either an X or Y chromosome. If the baby gets XX, it is a girl; if it gets XY, it is a boy. Thus, the father determines the sex of the newborn.

22. Do genetic combination of mothers play a significant role in determining the sex of a new born?

Answer: No, the mother’s genetic combination does not determine the sex of the newborn. The mother always provides an X chromosome, while the father provides either an X or Y chromosome. Therefore, the father’s chromosome determines whether the baby is a boy or a girl.

23. Why do all the gametes formed in human females have an X chromosome?

Answer: Human females have two X chromosomes (XX). During gamete formation (meiosis), only one sex chromosome goes into each egg cell. Since females do not have a Y chromosome, every egg formed carries only an X chromosome. Therefore, all gametes produced by human females have an X chromosome.

24. In human beings, the statistical probability of getting either a male or female child is 50 : 50. Give a suitable explanation.

Answer: In humans, females have XX chromosomes and males have XY chromosomes. The mother always contributes an X chromosome, while the father contributes either X or Y in equal numbers. Therefore, there is an equal chance of getting XX (girl) or XY (boy), making the probability 50 : 50.

31. A very small population of a species faces a greater threat of extinction than a larger population. Provide a suitable genetic explanation.

Answer: A very small population has limited genetic variation. Due to genetic drift, allele frequencies change randomly and harmful alleles may become fixed. Inbreeding increases, leading to expression of recessive deleterious traits. This reduces fertility and survival. A large population maintains higher variability and better adaptability to environmental changes, so it survives longer. Hence, small populations face higher risk of extinction due to reduced genetic diversity and adaptability in affected populations.

32. What are homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor?

Answer: Homologous structures are organs in different organisms that have similar basic structural design and origin but perform different functions. For example, the forelimbs of humans, whales, and bats. These structures indicate divergent evolution from a common ancestor. Yes, homologous structures generally suggest a common ancestor because they share the same basic plan, even though their functions have changed over time due to adaptation to different environments.

33. Does the occurrence of diversity of animals on earth suggest their diverse ancestry also? Discuss this point in the light of evolution.

Answer: No, diversity of animals on Earth does not always mean they have completely separate ancestry. According to evolution, most animals share a common origin but have diversified over time through gradual changes. This process is called evolution by common descent. Different environmental conditions led to adaptations, natural selection, and formation of new species. So, diverse animals are related through evolutionary branching rather than entirely different ancestries.

25. Give the pair of contrasting traits of the following characters in pea plant and mention which is dominant and recessive
(i) yellow seed           (ii) round seed

Answer: In pea plants, the pair of contrasting traits for the following characters are:

Character	Dominant Trait	Recessive Trait
(i) Yellow seed	Yellow seed	Green seed
(ii) Round seed	Round seed	Wrinkled seed

26. Why did Mendel choose pea plant for his experiments?

Answer:  Mendel chose the pea plant because:

(a) It had well-defined, observable contrasting traits (e.g., tall/dwarf, round/wrinkled).

(b) It is self-pollinating but can be cross-pollinated easily.

(c) It has a short life cycle, producing many offspring in one generation.

27. A woman has only daughters. Analyse the situation genetically and provide a suitable explanation.

Answer: A woman has only daughters because the father’s sperm carrying the X chromosome fertilised all her eggs. In humans, the mother (XX) always contributes an X chromosome, while the father (XY) can contribute either an X or a Y chromosome. When the father’s X chromosome fuses with the mother’s egg, it results in XX (female child). The birth of only daughters indicates that only X-bearing sperm fertilised the eggs. This is a matter of chance.

Long Answer Questions

37. Does geographical isolation of individuals of a species lead to formation of a new species? Provide a suitable explanation.

Answer: Yes, geographical isolation can lead to formation of a new species. When a population gets separated by physical barriers like mountains or rivers, gene flow between them stops. Over time, due to mutation, natural selection and genetic drift, the isolated groups accumulate genetic differences. Eventually, they become so different that they cannot interbreed, forming new species. This process is called speciation due to geographical isolation.

38. Bacteria have a simpler body plan when compared with human beings. Does it mean that human beings are more evolved than bacteria? Provide a suitable explanation.

Answer: No, human beings are not necessarily more evolved than bacteria. Evolution does not mean progress from simpler to complex forms in a linear fashion. Both bacteria and humans have evolved continuously for the same amount of time since life began. Bacteria are well-adapted to their environment and have survived for billions of years, showing they are equally evolved. Evolution simply results in populations being better suited to their specific habitats, not in becoming "higher" or "lower" organisms.

39. All the human races like Africans, Asians, Europeans, Americans and others might have evolved from a common ancestor. Provide a few evidences in support of this view.

Answer: Yes, there is strong scientific evidence that all human populations such as Africans, Asians, Europeans and Americans share a common ancestor.

A few important evidences are:

(a) Fossil evidence: Fossils of early humans like Homo sapiens and earlier ancestors such as Homo erectus and Australopithecus show a gradual evolutionary change. These fossils are found in different parts of the world, supporting the idea of migration from a single origin.

(b) Genetic evidence (DNA): Modern studies show that the DNA of all humans is about 99.9% similar. This very small variation indicates that all humans are closely related and must have come from a common ancestral population.

(c) Migration theory (Out of Africa): Scientific research suggests that modern humans first evolved in Africa and then migrated to other continents. As they spread, they adapted to different environments, leading to differences in skin colour, body features, etc.

(d) Ability to interbreed: All human groups, regardless of race or region, can interbreed and produce fertile offspring. This clearly shows they belong to the same species.

(e) Similar body structure: Basic anatomical features like number of bones, organ systems and brain structure are the same in all humans, supporting common origin.

40. Differentiate between inherited and acquired characters. Give one example for each type.

Answer: The difference between inherited and acquired characters are :

Inherited characters	Acquired characters
(i) These are traits passed from parents to offspring through genes.	(i) These are traits developed during an individual’s lifetime.
(ii) They are present since birth.	(ii) They are not present at birth.
(iii) They can be transferred to the next generation.	(iii) They cannot be transferred to the next generation
Example: Blood group in humans.	Example: Muscular body developed by exercise.

41. Give reasons why acquired characters are not inherited.

Answer: Acquired characters are not inherited because they are developed during an individual’s lifetime due to environmental influence or use and disuse of organs. These changes do not affect the DNA or genes present in the reproductive cells. Since only genetic information in germ cells is passed to the next generation, acquired traits are not transmitted. Therefore, only inherited genetic variations, not acquired changes, are passed from parents to offspring.

42. Evolution has exhibited a greater stability of molecular structure when compared with morphological structures. Comment on the statement and justify your opinion.

Answer: This statement is accurate because molecular structures, such as DNA and proteins, change very slowly over time due to their crucial role in basic life functions. In contrast, morphological (body) structures like limbs or beaks change more rapidly in response to environmental needs. For example, the DNA of humans and chimpanzees is about 98–99% similar, showing molecular stability, while their body shapes are quite different. Thus, molecular structure is more stable across generations than external form.

43. In the following crosses write the characteristics of the progeny

Cross	Progeny
(a) RR YY x RR YY Round, yellow Round, yellow	………………
(b) Rr Yy x Rr Yy Round, yellow Round, yellow	………………
(c) rr yy x rr yy wrinkled, green wrinkled, green	………………
(d) RR YY x rr yy Round, yellow wrinkled green	………………

Answer: The characteristics of the progeny are:

Cross	Progeny
(a) RR YY x RR YY Round, yellow × Round, yellow	All Round, yellow
(b) Rr Yy x Rr Yy Round, yellow × Round, yellow	Round, yellow : Round, green : Wrinkled, yellow : Wrinkled, green (9:3:3:1 ratio)
(c) rr yy x rr yy wrinkled, green × wrinkled, green	All Wrinkled, green
(d) RR YY x rr yy Round, yellow × Wrinkled, green	All Round, yellow (F1 generation)

44. Study the following cross and showing self pollination in , fill in the blank and answer the question that follows
  Parents             RRYY            x               rryy
                    Round, yellow                wrinkled, green
            —       Rr Yy             x               ?
                    Round, yellow

Answer:

Parents	RRYY                  ×             rryy    (Round, yellow)              (wrinkled, green)
	Rr Yy                 ×             Rr Yy (Round, yellow)              (Round, yellow)

The phenotypic ratio is 9 Round, yellow : 3 Round, green : 3 Wrinkled, yellow : 1 Wrinkled, green.

45. In question 44, what are the combinations of character in the F2 progeny? What are their ratios?

Answer: The combinations of characters are: Round yellow, Round green, Wrinkled yellow and Wrinkled green.

Their ratio is 9:3:3:1. This means that out of 16 offspring, 9 are round yellow, 3 are round green, 3 are wrinkled yellow, and 1 is wrinkled green.

This shows that the two traits (seed shape and seed colour) are inherited independently of each other.

46. Give the basic features of the mechanism of inheritance.

Answer: The basic features of the mechanism of inheritance are:

(i) Characters are controlled by genes which occur in pairs.

(ii) In a pair of genes, one may be dominant and the other recessive.

(iii) During gamete formation, the two genes of a pair separate from each other (segregation).

(iv) Genes for different traits are inherited independently of each other (independent assortment).

(v) The traits are passed from parents to offspring through the sex cells or gametes.

47. Give reasons for the appearance of new combinations of characters in the F₂ progeny.

Answer: New combinations of characters appear in the F₂ progeny due to the independent assortment of genes during gamete formation. In a dihybrid cross, the alleles of different traits segregate independently, forming different combinations of gametes. During fertilisation, these gametes combine randomly, producing new trait combinations. Crossing over during meiosis also contributes to variation. Hence, recombination of genes leads to new phenotypes in the F₂ generation.