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NCERT Solutions for Class 10th Science


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Chapter 9. Heredity and Evolution

Text-book Questions




Text-book Questions

Page no. 143

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?

Ans: The trait which was presented in previous generation will remain same under asexual reproduction, but there shall be some differences. Similarly, the trait which exists in more percentage, it must be presented in before. So trait B which exists in 60 % probably it likely to have arisen earlier.  

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

Ans: The species receive variation from their parents, while some variations are special in them, however which makes them special in nature. Different individuals in a species due to these differences may get advantages. Their survival will be fixed by nature to have accordingly variations. 

Page no. 147

Q1. How do Mendel’s experiments show that traits may be dominant or recessive?

Ans: According to Mendal's experiments, He selected two traits of pea which was tall pea plants and other was short pea plants as parents plants. In F1 generation all plants were tall, but in second generation called F2 three forth of pea plants were tall and one third were short. Both TT and Tt plants were tall while tt plants were only short, this experiments show that both traits were inherited but T trait for tallness was dominant and t trait for shortness was recessive. 

Q2. How do Mendel’s experiments show that traits are inherited

Ans: In Mendal's experiments show that all plants were tall in F1 generation. No one was short, while parents were taken both tall and short plants of traits. Surprisingly, There were one third plants were short. This shows that traits are inherited independently.

Q3. 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 traits – blood group A or O – is dominant? Why or why not?

Ans: Blood group O is dominant. The trait which appears is dominant in two trait blood group A and O. 

Q4. How is the sex of the child determined in human beings?

Ans: Sex chromosomes determines the sex in human being, in which there is only one pair sex chromosomes in human being. The males have XY chromosomes and the females have XX chromosomes. All children get X chromosome from their mother. So that is clear mother is no responsible for boy or girl. But Only Y chromosome of father determines sex of baby that will be boy or girl. 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.

Page no. 150

Q1. What are the different ways in which individuals with a particular trait may increase in a population?


(i) Using sexual reproduction which provide large numbers of variation. 

(ii) However changing in colour prevent species like beetals. 

(iii) Small species may be victims, so there is great possibility to survive a large species. 

Q2. Why are traits acquired during the life-time of an individual not inherited?

Ans: Dominant traits transfer from one generation to other generation by DNA. An individual do not use sexual reproduction. So This has no special reproductive cells to reproduce. Hence, the trait transfer to DNA through reproductive cells. So there is no chance to inherit aquired trait over generation. Therefore the experiences of an individual during its lifetime cannot
be passed on to its progeny.  

Q3. Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?

Ans: Any individual evolutes when this produces changes. Changes bring variations and variations are responsible for their survival. But tiger have no made so much changes in their species. This causes small number of tigers a cause of worry from the point of view of genetics. 

Page no. 151 

Q1. What factors could lead to the rise of a new species?

Ans: (i) Genetic drift and natural selection affect the variations and they become too much differ.  

(ii) Changing in Chromosomes causes the germ cells of the two groups cannot fuse with each other.. 

(iii) Changing in DNA . 

Q2. Will geographical isolation be a major factor in the speciation of a selfpollinating plant species? Why or why not?

Ans: Physical traits are affected by geograpgical isolation.

Q3. Will geographical isolation be a major factor in the speciation of an
organism that reproduces asexually? Why or why not? 


Page no. 156

Q1. Give an example of characteristics being used to determine how close
two species are in evolutionary terms.
Q2. Can the wing of a butterfly and the wing of a bat be considered
homologous organs? Why or why not?
Q3. What are fossils? What do they tell us about the process of evolution?

page no. 158 

Q1. 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?
Q2. In evolutionary terms, can we say which among bacteria, spiders, fish
and chimpanzees have a ‘better’ body design? Why or why not?




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