NCERT Solutions for Class 10 Science Chapter 9 Heredity and Evolution

1. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as

(a) TTWW (b) TTww (c) TtWW (d) TtWw

Answer: (c) TtWW

TtWW shows genetic makeup of tall plant. As all progeny bore violet flowers, shows that tall plant having violet flower has WW genotype for violet flowers. Progeny is both tall as well as short, therefore, parent plant must not be tall, it could have genotype Tt. Thus, half progeny is tall and all have violet flower.

2. An example of homologous organs is

(a) our arm and a dog’s fore-leg.

(b) our teeth and an elephant’s tusks.

(c) potato and runners of grass.

(d) all of the above.

Answer: b) our teeth and an elephant’s tusks

3. In evolutionary terms, we have more in common with

(a) a Chinese school-boy. (b) a chimpanzee. (c) a spider. (d) a bacterium.

Answer: (a) a Chinese school-boy

4. A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?

Answer: Consider children having light coloured eye have genotype LL Ll or ll. Therefore, if children with light coloured eye have LL genotype, therefore, their parents will also have genotype LL.

LL x LL

⬇️

LL

However, if children having light coloured eye have genotype ll, then their parents will also have genotype ll

ll x ll

⬇️

ll

Thus, it cannot be concluded whether if the light coloured eye children are dominant or recessive.

5. How are the areas of study – evolution and classification – interlinked?

Answer: Yes classification and evolution are interlinked. Grouping of organism on the basis of its characteristics, internal and external structure and evolution is called classification. If two species have common characteristics then they are closely related. However, if species are closely related then it suggest that they have common ancestors. A brother and sister may have common characteristics as they have common ancestors their parents. As more and more generation passes, the organism becomes different from their ancestors.

6. Explain the terms analogous and homologous organs with examples.

Answer: Organs similar in origin but perform different functions are called homologous organs. For example, skeletal structure of forelimb of humans and wings of birds are same, but externally they look like arms and wings respectively. Organs that have different origin but perform same function are called analogous organs. For example, wings of bat and bird are similar. But, it doesn’t suggest that both are related closely. Wings of bat are skin folded between their fingers, however, wings of birds are present along their arm. Thus, these organs are analogous organs.

7. Outline a project which aims to find the dominant coat colour in dogs.

Answer: Variety of genes in dogs are responsible for coat colour in dogs. Coat color in dogs is responsible for minimum eleven genes say A,B, C, D,E,F,G,M,P,S,T. One gene from each parent is inherited by the dog, therefore, phenotypes expresses the dominant gene. Take and example of B series, in which dog is genetically either brown or black. Consider the two parents be homozygous black BB and homozygous brown bb respectively.

Table

It can be noticed that all the offsprings are heterozygous Bb

Here B is dominant therefore all offspring will be black (B) but they will have B and b alleles. If such heterozygous offsprings are cross they will 25 % homozygous black (BB), 25% homozygous brown (bb) and 50% heterozygous black(Bb).

Table

8. Explain the importance of fossils in deciding evolutionary relationships.

Answer: Remains of dead organisms that once existed on the earth is called as fossil. Fossils are responsible for providing evidence of past organisms, changes occurred in past organisms that are reflected in present organisms. Hundred millions years ago, some invertebrates died and were buried in the ground. More and more sediments were deposited over it converting it into sedimentary rock. After few millions of years later, dinosaurs were buried in the same area. These were buried above the sedimentary rock. Soil covered on the dinosaurs was also turned into rock. More millions of years later, horse like animals died and got buried into the soil on the same area above the dinosaurs. Due to soil erosion or wind, the fossils of horse like animals got exposed. When the same area if digged further fossils of dinosaurs and invertebrates were found. This shows that fossils found closer to the surface of earth are most recent than those present deep within the earth.

9. What evidence do we have for the origin of life from inanimate matter?

Answer: Life is originated from simple organic molecule, this was first suggested by a British scientist J B Haldane. This was later proved by Stanley Miller and Harold Urey in 1953. A mixture of water, methane, ammonia and hydrogen gas was taken in the chamber in which electric sparks were passed through the electrodes. After a week 15% of carbon in methane was converted into amino acids, sugars, etc. These organic molecules undergoes polymerisation and has assembled to from life on the earth.

10. Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?

Answer: In sexual reproduction of DNA of two different individuals combine together to form new individual. Thus lots of variation is found in sexual reproduction. However, in asexual variation is found only when there is error in exact copying in DNA. Also if more variations are found in asexual reproduction then the newly formed DNA will not survive in the cell. However, in asexual reproduction resultant DNA survives and more variations are allowed, also it enhances the survival of cell.

Variants helps in survival of species in all conditions. Environmental conditions like heat, light and availability of food can change suddenly at one place. Variants that could resist the change survives, thereby causing more adaptive species. Therefore, variations helps in evolution of sexually reproducing organisms.

11. How is the equal genetic contribution of male and female parents ensured in the progeny?

Answer: In human beings the sex of the individual is genetically determined with the genes inherited from parents.

• Human beings have 22 chromosomes in matched pairs. The pair have same genes inherited from maternal i.e. from mother and another is paternal i.e. from father.
• In Human beings, males have all chromosomes in matched pairs except one, known as sex chromosome. represented as (XY)
• In females sex chromosomes are in matched pairs represented as (XX).
• Sex of the child is determined by the sex chromosome they inherit from the father.I.e. If child inherits X chromosome from father and X from mother then together it will form a female child i.e.( XX).
• But if child inherits Y chromosome from father and X chromosome from mother then it will form a male child i.e. (XY).

12. Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not?

Answer: Variation providing survival are naturally selected for a species. Variations helps individuals in the species to adjust in the surrounding and simultaneously these variations are passed to their progeny. This facilitates the evolution of organisms. There can be some variations which do not offer survival but has occurred accidentally. Such variation changes the frequency of genes. This change in frequency of genes for small population is called as genetic drift.

Check other lessons NCERT Solutions for Class 10

Download free NCERT textbook class 10 Science – Chapter 8 How do organisms reproduce ?