NCERT Solutions for Class 10 Science Chapter 9 Heredity And Evolution

Q1 ) If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?

Answer :

Trait B is likely to have arisen earlier because it is present in a larger percentage of the population.

Q2 ) How does the creation of variations in a species promote survival?

Answer :

The changes in the environment brings out Variations in the species. Such variations enable stability to the population of various species by preventing them from getting wiped out during adverse conditions. Thus, variations help a species in survival.

Q3 ) How do Mendel’s experiments show that the traits may be dominant or recessive?

Answer :

Mendel took pea plants with contrasting characteristics which included tall plant and dwarf (or short) plant. On cross pollination, he found all tall plants in the first generation \( F_1 \) and further by the self pollination of \( F_1 \) tall plants, he found that the plants of the second generation consisted of tall and short pants in the ratio of 3 : 1. On the basis of these experiments, the characteristics that appeared in the first generation were called dominant (i.e. tall plants) and the characteristics that did not appear were called recessive (i.e. dwarf plants).

Q4 ) How do Mendel’s experiments show that traits are inherited independently?

Answer :

Mendel took two pairs of alternate expressions of two traits and carried out hybrid crosses by crossing them and named the traits that appeared in the first generation as dominant. When he used these \( F_1 \) progeny to generate \( F_2 \) progeny by self-pollination, plants of different types were produced and saw that in some plants both the traits were dominant, while in some plants both were recessive and some plants exhibited mixed traits. This indicates that traits are inherited independently.

Q5 ) A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the trait – blood group A or O – is dominant? Why or why not?

Answer :

This information is not sufficient. This is because each individual is carrying two alleles and the recessive trait can occur only when alleles are similar.For considering a trait as dominant or recessive, data of three generations is required but here we have data of only two generations.

Q6 ) How is the sex of a child determined in human beings?

Answer :

Somatic cells in human beings contain 23 pairs of chromosomes. Out of them the 23rd pair is composed of X and Y chromosomes. In males, the 23rd pair contains one X and one Y chromosome. On the other hand, in a female the 23rd pair only contains X chromosomes. This means that the eggs would have X chromosome as the 23rd chromosome, while a sperm may have either X or Y chromosome as the 23rd chromosome. When a sperm with X chromosome fertilizes the egg, female child would be developed by the formed zygote. When a sperm with Y chromosome fertilizes the egg, the resulting zygote would develop into a male child.Thus, there are 50 – 50 chances of a male or female child and none of the parents may by responsible for the Sex determination in humans.

Q7 ) What are the different ways in which individuals with a particular trait may increase in a population?

Answer :

Different ways in which individuals with a particular trait may increase in a population are as follows :

(i) If it gives the benefit of survival through natural selection. For e.g. blue beetles could not be spotted by the crows hence more blue beetles could survive.

(ii)Due to genetic drift, a sudden increase in a particular trait in a population.

Q8 ) Why are traits acquired during the lifetime of an individual not inherited?

Answer :

Acquired traits during the lifetime of an individual do not bring any change in the genotype of an individual i.e, no changes occur in the reproductive cells of the organisms and are not capable of being passed on to the next generation. Hence, acquired traits do not get inherited.

Q9 ) Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?

Answer :

The small numbers of surviving tigers is a cause of worry from the point of view of genetics because there are negligible genetic variations if there is a small number of population. Due to this they are not well adapted in the rapid environmental changes which are not favourable for them. If these changes are not controlled, a time may come when lack of useful variations may result in extinction of tigers.

Q10 ) What factors could lead to the rise of a new species?

Answer :

Rise in new species can happen if two groups of the same species are somehow prevented from interbreeding for several generations. This can happen because of geographical isolation or because of some genetic drifts.Geographical isolation of a population caused by various barriers (such as mountain ranges, rivers and sea) which leads to reproductive isolation due to which there is no flow of genes between separated groups of population.Also the Genetic drift caused by drastic changes in the frequencies of particular genes alone can also be the reason.

Q11 ) Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?

Answer :

The geographical isolation cannot be a major factor in the speciation of a self-pollinating plant species because in the process of reproduction to be carried out it does not have to look at the other plants i.e, no new trait can become a part of the genotype in self-pollination plant species.However, there are chances of some variation that can occur due to the change in environment..

Q12 ) Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not ?

Answer :

Geographical isolation cannot be a major factor in the speciation of an asexually reproducing organism because it does not require any other organism to carry out reproduction i.e, there is no exchange of genetic material with the other species in such organisms..

Q13 ) Give an example of characteristics being used to determine how close two species are in evolutionary terms.

Answer :

If similar characteristics are shown in different organisms, then these are considered to be inherited from the common ancestry. It also shows the closeness of the species.For example, humans and apes have some similarity in their body designs, so they are closely related in evolutionary terms.Now take humans and fishes which have vertebral columns,brain box etc as common but look completely different from each other. Hence they are not closely related rather they are like distant relatives.

Q14 ) Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not?

Answer :

The wings of a butterfly and the wings of a bat cannot be considered to be homologous though they are used for the same purpose of flying organs because they have different basic designs.Wings of a butterfly are composed of chitinous membrane, while wings of a bat are composed of bony skeleton. They are analogous organs.

Q15 ) What are fossils? What do they tell us about the process of evolution?

Answer :

Fossils: Fossils are the remains or traces of a dead organism from the distant past. They tell about the changes and development that occurred on the earth’s surface and to the complex structured organisms from simple structured organisms.They exhibit the process of human evolution and states that angiosperms are developed from pteridophytes and gymnosperms and many more details which helps to understand the evolution and changes in environment.

Q16 ) Why are human beings who look so different from each other in terms of size, colour and looks said to belong to the same species?

Answer :

In spite of wide differences in size, colour and looks, human beings can interbreed i.e, they can reproduce among themselves and produce fertile offspring which says that there is no reproductive isolation. Hence, all of them are kept under one species.

Q17 ) In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design? Why or why not?

Answer :

It depends on our consideration of ‘better’ design.If criteria like complexity of body design is considered, then chimpanzees are obviously better than bacteria. But if the criteria is ability of survival in all kinds of habitat then bacteria are far ahead than any other group of organisms.