Heredity and Evolution Class 10 Notes | EduRev

Class 10 : Heredity and Evolution Class 10 Notes | EduRev

 Page 1


www.ncrtsolutions.in  
 
www.ncrtsolutions.in  
 
 Heredity and Evolution 
Question 1: 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: In asexual reproduction, the reproducing cells produce a copy of their DNA through 
some chemical reactions. However, this copying of DNA is not accurate and therefore, the newly 
formed DNA has some variations. 
  
 
  
It can be easily observed in the above figure that in asexual reproduction, very few variations are 
allowed. Therefore, if a trait is present in only 10% of the population, it is more likely that the trait 
has arisen recently. Hence, it can be concluded that trait B that exists in 60% of the same 
population has arisen earlier than trait A. 
  
Question 2: How does the creation of variations in a species promote survival? 
  
Answer: Sometimes for a species, the environmental conditions change so drastically that their 
survival becomes difficult. For example, if the temperature of water increases suddenly, most of 
the bacteria living in that water would die. Only few variants resistant to heat would be able to 
survive. If these variants were not there, then the entire species of bacteria would have been 
destroyed. Thus, these variants help in the survival of the species. 
  
However, not all variations are useful. Therefore, these are not necessarily beneficial for the 
individual organisms. 
  
Question 3: How do Mendel’s experiments show that traits may be dominant or recessive? 
  
Answer: Mendel selected true breeding tall (TT) and dwarf (tt) pea plants. Then, he crossed these 
two plants. The seeds formed after fertilization were grown and these plants that were formed 
represent the first filial or F1 generation. All the F1 plants obtained were tall. 
  
 
 
 
   
Page 2


www.ncrtsolutions.in  
 
www.ncrtsolutions.in  
 
 Heredity and Evolution 
Question 1: 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: In asexual reproduction, the reproducing cells produce a copy of their DNA through 
some chemical reactions. However, this copying of DNA is not accurate and therefore, the newly 
formed DNA has some variations. 
  
 
  
It can be easily observed in the above figure that in asexual reproduction, very few variations are 
allowed. Therefore, if a trait is present in only 10% of the population, it is more likely that the trait 
has arisen recently. Hence, it can be concluded that trait B that exists in 60% of the same 
population has arisen earlier than trait A. 
  
Question 2: How does the creation of variations in a species promote survival? 
  
Answer: Sometimes for a species, the environmental conditions change so drastically that their 
survival becomes difficult. For example, if the temperature of water increases suddenly, most of 
the bacteria living in that water would die. Only few variants resistant to heat would be able to 
survive. If these variants were not there, then the entire species of bacteria would have been 
destroyed. Thus, these variants help in the survival of the species. 
  
However, not all variations are useful. Therefore, these are not necessarily beneficial for the 
individual organisms. 
  
Question 3: How do Mendel’s experiments show that traits may be dominant or recessive? 
  
Answer: Mendel selected true breeding tall (TT) and dwarf (tt) pea plants. Then, he crossed these 
two plants. The seeds formed after fertilization were grown and these plants that were formed 
represent the first filial or F1 generation. All the F1 plants obtained were tall. 
  
 
 
 
   
www.ncrtsolutions.in  
 
www.ncrtsolutions.in  
 
 
  
Cross-pollination of tall and short plant 
  
Then, Mendel self-pollinated the F1 plants and observed that all plants obtained in the 
F2 generation were not tall. Instead, one-fourth of the F2 plants were short. 
  
 
  
Self-pollination of F1 plants 
  
From this experiment, Mendel concluded that the F1 tall plants were not true breeding. They were 
carrying traits of both short height and tall height. They appeared tall only because the tall trait is 
dominant over the dwarf trait. 
  
Question 4: How do Mendel’s experiments show that traits are inheritedindependently? 
  
Answer: Mendel crossed pea plants having round green seeds (RRyy) with pea plants having 
wrinkled yellow seeds (rrYY). 
  
Page 3


www.ncrtsolutions.in  
 
www.ncrtsolutions.in  
 
 Heredity and Evolution 
Question 1: 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: In asexual reproduction, the reproducing cells produce a copy of their DNA through 
some chemical reactions. However, this copying of DNA is not accurate and therefore, the newly 
formed DNA has some variations. 
  
 
  
It can be easily observed in the above figure that in asexual reproduction, very few variations are 
allowed. Therefore, if a trait is present in only 10% of the population, it is more likely that the trait 
has arisen recently. Hence, it can be concluded that trait B that exists in 60% of the same 
population has arisen earlier than trait A. 
  
Question 2: How does the creation of variations in a species promote survival? 
  
Answer: Sometimes for a species, the environmental conditions change so drastically that their 
survival becomes difficult. For example, if the temperature of water increases suddenly, most of 
the bacteria living in that water would die. Only few variants resistant to heat would be able to 
survive. If these variants were not there, then the entire species of bacteria would have been 
destroyed. Thus, these variants help in the survival of the species. 
  
However, not all variations are useful. Therefore, these are not necessarily beneficial for the 
individual organisms. 
  
Question 3: How do Mendel’s experiments show that traits may be dominant or recessive? 
  
Answer: Mendel selected true breeding tall (TT) and dwarf (tt) pea plants. Then, he crossed these 
two plants. The seeds formed after fertilization were grown and these plants that were formed 
represent the first filial or F1 generation. All the F1 plants obtained were tall. 
  
 
 
 
   
www.ncrtsolutions.in  
 
www.ncrtsolutions.in  
 
 
  
Cross-pollination of tall and short plant 
  
Then, Mendel self-pollinated the F1 plants and observed that all plants obtained in the 
F2 generation were not tall. Instead, one-fourth of the F2 plants were short. 
  
 
  
Self-pollination of F1 plants 
  
From this experiment, Mendel concluded that the F1 tall plants were not true breeding. They were 
carrying traits of both short height and tall height. They appeared tall only because the tall trait is 
dominant over the dwarf trait. 
  
Question 4: How do Mendel’s experiments show that traits are inheritedindependently? 
  
Answer: Mendel crossed pea plants having round green seeds (RRyy) with pea plants having 
wrinkled yellow seeds (rrYY). 
  
www.ncrtsolutions.in  
 
www.ncrtsolutions.in  
 
 
  
An example of dihybrid crosses 
  
Since the F1 plants are formed after crossing pea plants having green round seeds and pea plants 
having yellow wrinkled seeds, F1 generation will have both these characters in them. However, as 
we know that yellow seed colour and round seeds are dominant characters, therefore, the F1 plants 
will have yellow round seeds. 
  
Then this F1 progeny was self-pollinated and the F2 progeny was found to have yellow round 
seeds, green round seeds, yellow wrinkled seeds, and green wrinkled seeds in the ratio of 9:3:3:1. 
  
 
  
Independent inheritance of two different traits 
  
In the above cross, more than two factors are involved, and these are independently inherited. 
  
Question 4: 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? 
  
Page 4


www.ncrtsolutions.in  
 
www.ncrtsolutions.in  
 
 Heredity and Evolution 
Question 1: 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: In asexual reproduction, the reproducing cells produce a copy of their DNA through 
some chemical reactions. However, this copying of DNA is not accurate and therefore, the newly 
formed DNA has some variations. 
  
 
  
It can be easily observed in the above figure that in asexual reproduction, very few variations are 
allowed. Therefore, if a trait is present in only 10% of the population, it is more likely that the trait 
has arisen recently. Hence, it can be concluded that trait B that exists in 60% of the same 
population has arisen earlier than trait A. 
  
Question 2: How does the creation of variations in a species promote survival? 
  
Answer: Sometimes for a species, the environmental conditions change so drastically that their 
survival becomes difficult. For example, if the temperature of water increases suddenly, most of 
the bacteria living in that water would die. Only few variants resistant to heat would be able to 
survive. If these variants were not there, then the entire species of bacteria would have been 
destroyed. Thus, these variants help in the survival of the species. 
  
However, not all variations are useful. Therefore, these are not necessarily beneficial for the 
individual organisms. 
  
Question 3: How do Mendel’s experiments show that traits may be dominant or recessive? 
  
Answer: Mendel selected true breeding tall (TT) and dwarf (tt) pea plants. Then, he crossed these 
two plants. The seeds formed after fertilization were grown and these plants that were formed 
represent the first filial or F1 generation. All the F1 plants obtained were tall. 
  
 
 
 
   
www.ncrtsolutions.in  
 
www.ncrtsolutions.in  
 
 
  
Cross-pollination of tall and short plant 
  
Then, Mendel self-pollinated the F1 plants and observed that all plants obtained in the 
F2 generation were not tall. Instead, one-fourth of the F2 plants were short. 
  
 
  
Self-pollination of F1 plants 
  
From this experiment, Mendel concluded that the F1 tall plants were not true breeding. They were 
carrying traits of both short height and tall height. They appeared tall only because the tall trait is 
dominant over the dwarf trait. 
  
Question 4: How do Mendel’s experiments show that traits are inheritedindependently? 
  
Answer: Mendel crossed pea plants having round green seeds (RRyy) with pea plants having 
wrinkled yellow seeds (rrYY). 
  
www.ncrtsolutions.in  
 
www.ncrtsolutions.in  
 
 
  
An example of dihybrid crosses 
  
Since the F1 plants are formed after crossing pea plants having green round seeds and pea plants 
having yellow wrinkled seeds, F1 generation will have both these characters in them. However, as 
we know that yellow seed colour and round seeds are dominant characters, therefore, the F1 plants 
will have yellow round seeds. 
  
Then this F1 progeny was self-pollinated and the F2 progeny was found to have yellow round 
seeds, green round seeds, yellow wrinkled seeds, and green wrinkled seeds in the ratio of 9:3:3:1. 
  
 
  
Independent inheritance of two different traits 
  
In the above cross, more than two factors are involved, and these are independently inherited. 
  
Question 4: 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? 
  
www.ncrtsolutions.in  
 
www.ncrtsolutions.in  
 
Answer: No. This information is not sufficient to determine which of the traits - blood group A 
or O - is dominant. This is because we do not know about the blood group of all the progeny. 
  
Blood group A can be genotypically AA or AO. Hence, the information is incomplete to draw any 
such conclusion. 
  
Question 5: How is the sex of the child determined in human beings? 
  
Answer: In human beings, the females have two X chromosomes and the males have one X and 
one Y chromosome. Therefore, the females are XX and the males are XY. 
  
The gametes, as we know, receive half of the chromosomes. The male gametes have 22 autosomes 
and either X or Y sex chromosome. 
  
Type of male gametes: 22+X OR 22+ Y. 
  
However, since the females have XX sex chromosomes, their gametes can only have X sex 
chromosome. 
  
Type of female gamete: 22+ X 
  
 
  
Sex determination in humans 
  
Thus, the mother provides only X chromosomes. The sex of the baby is determined by the type of 
male gamete (X or Y) that fuses with the X chromosome of the female. 
  
Question 6: What are the different ways in which individuals with a particular trait may increase 
in a population? 
  
Answer: Individuals with a particular trait may increase in a population as a result of  the 
following: 
  
(i) Natural selection: When that trait offers some survival advantage. 
  
(ii) Genetic drift: When some genes governing that trait become common in a population. 
  
(iii) When that trait gets acquired during the individual’s lifetime. 
  
Question 7: Why are traits acquired during the life-time of an individual not inherited? 
Page 5


www.ncrtsolutions.in  
 
www.ncrtsolutions.in  
 
 Heredity and Evolution 
Question 1: 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: In asexual reproduction, the reproducing cells produce a copy of their DNA through 
some chemical reactions. However, this copying of DNA is not accurate and therefore, the newly 
formed DNA has some variations. 
  
 
  
It can be easily observed in the above figure that in asexual reproduction, very few variations are 
allowed. Therefore, if a trait is present in only 10% of the population, it is more likely that the trait 
has arisen recently. Hence, it can be concluded that trait B that exists in 60% of the same 
population has arisen earlier than trait A. 
  
Question 2: How does the creation of variations in a species promote survival? 
  
Answer: Sometimes for a species, the environmental conditions change so drastically that their 
survival becomes difficult. For example, if the temperature of water increases suddenly, most of 
the bacteria living in that water would die. Only few variants resistant to heat would be able to 
survive. If these variants were not there, then the entire species of bacteria would have been 
destroyed. Thus, these variants help in the survival of the species. 
  
However, not all variations are useful. Therefore, these are not necessarily beneficial for the 
individual organisms. 
  
Question 3: How do Mendel’s experiments show that traits may be dominant or recessive? 
  
Answer: Mendel selected true breeding tall (TT) and dwarf (tt) pea plants. Then, he crossed these 
two plants. The seeds formed after fertilization were grown and these plants that were formed 
represent the first filial or F1 generation. All the F1 plants obtained were tall. 
  
 
 
 
   
www.ncrtsolutions.in  
 
www.ncrtsolutions.in  
 
 
  
Cross-pollination of tall and short plant 
  
Then, Mendel self-pollinated the F1 plants and observed that all plants obtained in the 
F2 generation were not tall. Instead, one-fourth of the F2 plants were short. 
  
 
  
Self-pollination of F1 plants 
  
From this experiment, Mendel concluded that the F1 tall plants were not true breeding. They were 
carrying traits of both short height and tall height. They appeared tall only because the tall trait is 
dominant over the dwarf trait. 
  
Question 4: How do Mendel’s experiments show that traits are inheritedindependently? 
  
Answer: Mendel crossed pea plants having round green seeds (RRyy) with pea plants having 
wrinkled yellow seeds (rrYY). 
  
www.ncrtsolutions.in  
 
www.ncrtsolutions.in  
 
 
  
An example of dihybrid crosses 
  
Since the F1 plants are formed after crossing pea plants having green round seeds and pea plants 
having yellow wrinkled seeds, F1 generation will have both these characters in them. However, as 
we know that yellow seed colour and round seeds are dominant characters, therefore, the F1 plants 
will have yellow round seeds. 
  
Then this F1 progeny was self-pollinated and the F2 progeny was found to have yellow round 
seeds, green round seeds, yellow wrinkled seeds, and green wrinkled seeds in the ratio of 9:3:3:1. 
  
 
  
Independent inheritance of two different traits 
  
In the above cross, more than two factors are involved, and these are independently inherited. 
  
Question 4: 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? 
  
www.ncrtsolutions.in  
 
www.ncrtsolutions.in  
 
Answer: No. This information is not sufficient to determine which of the traits - blood group A 
or O - is dominant. This is because we do not know about the blood group of all the progeny. 
  
Blood group A can be genotypically AA or AO. Hence, the information is incomplete to draw any 
such conclusion. 
  
Question 5: How is the sex of the child determined in human beings? 
  
Answer: In human beings, the females have two X chromosomes and the males have one X and 
one Y chromosome. Therefore, the females are XX and the males are XY. 
  
The gametes, as we know, receive half of the chromosomes. The male gametes have 22 autosomes 
and either X or Y sex chromosome. 
  
Type of male gametes: 22+X OR 22+ Y. 
  
However, since the females have XX sex chromosomes, their gametes can only have X sex 
chromosome. 
  
Type of female gamete: 22+ X 
  
 
  
Sex determination in humans 
  
Thus, the mother provides only X chromosomes. The sex of the baby is determined by the type of 
male gamete (X or Y) that fuses with the X chromosome of the female. 
  
Question 6: What are the different ways in which individuals with a particular trait may increase 
in a population? 
  
Answer: Individuals with a particular trait may increase in a population as a result of  the 
following: 
  
(i) Natural selection: When that trait offers some survival advantage. 
  
(ii) Genetic drift: When some genes governing that trait become common in a population. 
  
(iii) When that trait gets acquired during the individual’s lifetime. 
  
Question 7: Why are traits acquired during the life-time of an individual not inherited? 
www.ncrtsolutions.in  
 
www.ncrtsolutions.in  
 
  
Answer: This happens because an acquired trait involves change in non-reproductive tissues 
(somatic cells) which cannot be passed on to germ cells or the progeny. Therefore, these traits 
cannot be inherited. 
  
Question 8: Why are the small numbers of surviving tigers a cause of worry from the point of 
view of genetics? 
  
Small numbers of tigers means that fewer variations in terms of genes are available. This means 
that when these tigers reproduce, there are less chances of producing progeny with some useful 
variations. Hence, it is a cause of worry from the point of view of genetics. 
  
Question 9: What factors could lead to the rise of a new species? 
  
Answer: Natural selection, genetic drift and acquisition of traits during the life time of an 
individual can give rise to new species. ill geographical isolation be a major factor in the 
speciation of a self-pollinating plant species? Why or why not? Geographical isolation can prevent 
the transfer of pollens among different plants. However, since the plants are self-pollinating, 
which means that the pollens are transferred from the anther of one flower to the stigma of the 
same flower or of another flower of the same plant, geographical isolation cannot prevent 
speciation in this case. 
  
Question 10: Will geographical isolation be a major factor in the speciation of an organism that 
reproduces asexually? Why or why not? 
  
Answer: Geographical isolation prevents gene flow between populations of a species whereas 
asexual reproduction generally involves only one individual. In an asexually reproducing 
organism, variations can occur only when the copying of DNA is not accurate. Therefore, 
geographical isolation cannot prevent the formation of new species in an asexually reproducing 
organism. 
  
Question 11: Give an example of characteristics being used to determine how close two species 
are in evolutionary terms. 
  
Answer: The presence of feathers in dinosaurs and birds indicates that they are evolutionarily 
related. Dinosaurs had feathers not for flying but instead these feathers provided insulation to 
these warm-blooded animals. However, the feathers in birds are used for flight. This proves that 
reptiles and birds are closely related and that the evolution of wings started in reptiles. 
  
Question 12: Can the wing of a butterfly and the wing of a bat be considered homologous organs? 
Why or why not? 
  
Answer: The wing of a butterfly and the wing of a bat are similar in function. They help the 
butterfly and the bat in flying. Since they perform similar function, they are analogous organs and 
not homologous. 
  
Question 13: What are fossils? What do they tell us about the process of evolution? 
  
Answer: Fossils are the remains of organisms that once existed on earth. They represent the 
ancestors of plants and animals that are alive today. They provide evidences of evolution by 
revealing the characteristics of the past organism and the changes that have occurred in these 
organisms to give rise to the present organisms. 
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