NCERT Solutions: Chapter - 9 - Heredity and evolution, Class 10, Science Class 10 Notes | EduRev

Created by: Appar Malik

Class 10 : NCERT Solutions: Chapter - 9 - Heredity and evolution, Class 10, Science Class 10 Notes | EduRev

 Page 1


    NCERT Solutions  
Heredity and evolution  
 
Ape man evolution 
 
 
Q1: Define Heredity. 
 
Answer: Heredity refers to the process by which certain features (heritable characteristics) are 
transmitted from parent to offspring. 
 
Q2: Define Variation. 
 
Answer: Offsprings of same parents do not exactly resemble each other as well as to their parents. It 
is known as variation. 
 
 
 
Q3(NCERT): 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. In asexual reproduction the traits which are present in previous generation are 
carried over to next generation with minor variations. Therefore the traits present in higher percentage 
have higher chances of persisting earlier.  
 
Q4(NCERT): How does the creation of variations in a species promote survival? 
 
Answer: Depending on the nature of variations different individuals would have different kinds of 
advantage e.g., Bacteria variants which can tolerate heat have better survival chances in heat wave in 
comparison to non-variant bacteria having no capacity to tolerate heat wave. 
However not all variations are useful or beneficial.  
Significance of Variation: 
1. It is the source of raw material for evolution. 
2. Animals are able to adapt themselves to the changing environment. 
3. Organisms are better suited to face the struggle for existence. 
4. Variations give the organisms an individuality of their own. 
5. Without variation, there would be no science of heredity as all individuals of a race, would be 
identical in all aspects. 
 
 
Note: Mendel postulated laws of inheritance using Quantitative approach. 
In 1860s, Gregor Mendel formulated a theory of inheritance based on experiments with garden peas, proposing 
that parents pass on to their offspring discrete hereditary factors (now called genes or alleles) that retain their 
identity through generations. Note Mendel did not call them genes. Later in 1909 Danish botanist Wilhelm 
Johannsen named these presumed hereditary particles “genes.” 
 
 
Page 2


    NCERT Solutions  
Heredity and evolution  
 
Ape man evolution 
 
 
Q1: Define Heredity. 
 
Answer: Heredity refers to the process by which certain features (heritable characteristics) are 
transmitted from parent to offspring. 
 
Q2: Define Variation. 
 
Answer: Offsprings of same parents do not exactly resemble each other as well as to their parents. It 
is known as variation. 
 
 
 
Q3(NCERT): 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. In asexual reproduction the traits which are present in previous generation are 
carried over to next generation with minor variations. Therefore the traits present in higher percentage 
have higher chances of persisting earlier.  
 
Q4(NCERT): How does the creation of variations in a species promote survival? 
 
Answer: Depending on the nature of variations different individuals would have different kinds of 
advantage e.g., Bacteria variants which can tolerate heat have better survival chances in heat wave in 
comparison to non-variant bacteria having no capacity to tolerate heat wave. 
However not all variations are useful or beneficial.  
Significance of Variation: 
1. It is the source of raw material for evolution. 
2. Animals are able to adapt themselves to the changing environment. 
3. Organisms are better suited to face the struggle for existence. 
4. Variations give the organisms an individuality of their own. 
5. Without variation, there would be no science of heredity as all individuals of a race, would be 
identical in all aspects. 
 
 
Note: Mendel postulated laws of inheritance using Quantitative approach. 
In 1860s, Gregor Mendel formulated a theory of inheritance based on experiments with garden peas, proposing 
that parents pass on to their offspring discrete hereditary factors (now called genes or alleles) that retain their 
identity through generations. Note Mendel did not call them genes. Later in 1909 Danish botanist Wilhelm 
Johannsen named these presumed hereditary particles “genes.” 
 
 
Q5: Name the two laws of inheritance postulated by Mendel? 
 
Answer: 
1. The Law of Segregation 
2. The law of Independent Assortment 
 
Q6: How do Mendel’s experiments show that traits may be dominant or recessive? 
 
Answer: Mendel took one tall pea (TT) plant and one short pea (tt) plant and produced progeny from 
them. The plants grown from F1 seeds represent first filial (F1) generation. All F1 plants were tall. 
Then Mendel self-pollinated F1 plants and found that all plants obtained in F2 progeny were not tall. 
Instead 75% were tall (dominant) while remaining 25% were dwarf (recessive traits). 
From the experiment, he concluded the F1 progeny is not a true breed but carries both traits. He 
concluded one trait is dominant over the other, that's why plants appear tall. It is also called the law of 
Segregation. 
 
 
 
Q7: How do Mendel’s experiments show that traits are inherited independently? 
 
Answer: When a pea plant of round green (RRyy) seeds is crossed with a pea plant having wrinkled 
yellow seeds (rrYY), plants in F1 progeny have round and yellow seeds. However in F2 generation, all 
traits appear independently. In F2, he got the following result (called dihybrid ratio): 
Round Yellow - 9 
Round Green - 3 
Wrinkled Yellow - 3 
Wrinkled Green - 1 
He concluded alleles controlling different traits are not linked and are inherited independently. It is 
also known as Law of Independent Assortment. 
 
Q8(NCERT): 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? 
 
Answer: No the information does not suffice. The blood group is determined by a pair of genes. It 
might happen the gene responsible for O group in the daughter might be inherited from mother or 
from father. For example, one possibility is father having AO pair and mother has OO pair of genes. 
 
Q9: Define allelomorph. 
 
Page 3


    NCERT Solutions  
Heredity and evolution  
 
Ape man evolution 
 
 
Q1: Define Heredity. 
 
Answer: Heredity refers to the process by which certain features (heritable characteristics) are 
transmitted from parent to offspring. 
 
Q2: Define Variation. 
 
Answer: Offsprings of same parents do not exactly resemble each other as well as to their parents. It 
is known as variation. 
 
 
 
Q3(NCERT): 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. In asexual reproduction the traits which are present in previous generation are 
carried over to next generation with minor variations. Therefore the traits present in higher percentage 
have higher chances of persisting earlier.  
 
Q4(NCERT): How does the creation of variations in a species promote survival? 
 
Answer: Depending on the nature of variations different individuals would have different kinds of 
advantage e.g., Bacteria variants which can tolerate heat have better survival chances in heat wave in 
comparison to non-variant bacteria having no capacity to tolerate heat wave. 
However not all variations are useful or beneficial.  
Significance of Variation: 
1. It is the source of raw material for evolution. 
2. Animals are able to adapt themselves to the changing environment. 
3. Organisms are better suited to face the struggle for existence. 
4. Variations give the organisms an individuality of their own. 
5. Without variation, there would be no science of heredity as all individuals of a race, would be 
identical in all aspects. 
 
 
Note: Mendel postulated laws of inheritance using Quantitative approach. 
In 1860s, Gregor Mendel formulated a theory of inheritance based on experiments with garden peas, proposing 
that parents pass on to their offspring discrete hereditary factors (now called genes or alleles) that retain their 
identity through generations. Note Mendel did not call them genes. Later in 1909 Danish botanist Wilhelm 
Johannsen named these presumed hereditary particles “genes.” 
 
 
Q5: Name the two laws of inheritance postulated by Mendel? 
 
Answer: 
1. The Law of Segregation 
2. The law of Independent Assortment 
 
Q6: How do Mendel’s experiments show that traits may be dominant or recessive? 
 
Answer: Mendel took one tall pea (TT) plant and one short pea (tt) plant and produced progeny from 
them. The plants grown from F1 seeds represent first filial (F1) generation. All F1 plants were tall. 
Then Mendel self-pollinated F1 plants and found that all plants obtained in F2 progeny were not tall. 
Instead 75% were tall (dominant) while remaining 25% were dwarf (recessive traits). 
From the experiment, he concluded the F1 progeny is not a true breed but carries both traits. He 
concluded one trait is dominant over the other, that's why plants appear tall. It is also called the law of 
Segregation. 
 
 
 
Q7: How do Mendel’s experiments show that traits are inherited independently? 
 
Answer: When a pea plant of round green (RRyy) seeds is crossed with a pea plant having wrinkled 
yellow seeds (rrYY), plants in F1 progeny have round and yellow seeds. However in F2 generation, all 
traits appear independently. In F2, he got the following result (called dihybrid ratio): 
Round Yellow - 9 
Round Green - 3 
Wrinkled Yellow - 3 
Wrinkled Green - 1 
He concluded alleles controlling different traits are not linked and are inherited independently. It is 
also known as Law of Independent Assortment. 
 
Q8(NCERT): 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? 
 
Answer: No the information does not suffice. The blood group is determined by a pair of genes. It 
might happen the gene responsible for O group in the daughter might be inherited from mother or 
from father. For example, one possibility is father having AO pair and mother has OO pair of genes. 
 
Q9: Define allelomorph. 
 
Answer: The contrasting pair of genes or alleles constitute an allelomorph. Examples : Tall and dwarf 
plants, wrinkled and smooth seed coat, white and violet coloured flower. 
 
Q10: What are different types of variations? 
 
Answer: There are two types: 
1. Somatic Variation - It pertains to body cells and it is not inherited. 
2. Germinal Variation - It pertains to germ cells or gametes and it is inheritable. It leads to speciation 
and evolution. 
 
 
Q11(CBSE exam): How one change adopted can perform different functions? 
 
Answer: The study of evolution reveals, one change occurred initially is used to perform other 
functions. For example, initially feathers were evolved for warmth, later they were adapted for flight. 
 
 
Q12: What do you mean by evolution? 
 
Answer: Evolution may be defined as a gradual development of more complex species from pre-
existing simpler forms. 
It is an extremely slow process and has occurred over millions of years,as revealed by fossil 
evidences. 
Evolution has thus resulted in the diversity of organisms, influenced by environmental selection. 
 
Q13(NCERT): How is the sex of the child determined in human beings? 
 
Answer: Normal human somatic cells are diploid. They have 46 chromosomes made up of two sets 
of23-one set from each parent. In human diploid cells, there are 22 homologous pairs of autosomes, 
each with a maternal and a paternal homolog. The 23rd pair, the sex chromosomes, determines 
whether the person is female (XX) or male (XY). 
 
Mother provides only X chromosomes. The sex of the child is determined by the type of chromosome 
(X or Y) received from male gamete. 
 
 
Q14(NCERT): What are the different ways in which individuals with a particular trait may increase 
in a population? 
 
Answer: 
1. Natural Selection: Certain variations give survival chances to individuals in a population in a 
changed situation resulting in increase of their population. 
2. Genetic drift: Accidents in small population even if they give no survival advantage, may lead to an 
increase of certain individuals in population. 
 
Q15: Why are traits acquired during the life-time of an individual not inherited? 
 
Answer: Any changes in somatic cells (or non-reproductive tissues) cannot be passed to DNA of germ 
cells. Hence these traits are not inheritable. 
 
 
Q16: Define Homozygous. 
 
Answer: An organism that has a pair of identical alleles for a character is said to be homozygous for 
the gene controlling that character.Homozygous plants "breed true" because all of their gametes 
contain the same allele- either TT or tt for example. 
 
Page 4


    NCERT Solutions  
Heredity and evolution  
 
Ape man evolution 
 
 
Q1: Define Heredity. 
 
Answer: Heredity refers to the process by which certain features (heritable characteristics) are 
transmitted from parent to offspring. 
 
Q2: Define Variation. 
 
Answer: Offsprings of same parents do not exactly resemble each other as well as to their parents. It 
is known as variation. 
 
 
 
Q3(NCERT): 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. In asexual reproduction the traits which are present in previous generation are 
carried over to next generation with minor variations. Therefore the traits present in higher percentage 
have higher chances of persisting earlier.  
 
Q4(NCERT): How does the creation of variations in a species promote survival? 
 
Answer: Depending on the nature of variations different individuals would have different kinds of 
advantage e.g., Bacteria variants which can tolerate heat have better survival chances in heat wave in 
comparison to non-variant bacteria having no capacity to tolerate heat wave. 
However not all variations are useful or beneficial.  
Significance of Variation: 
1. It is the source of raw material for evolution. 
2. Animals are able to adapt themselves to the changing environment. 
3. Organisms are better suited to face the struggle for existence. 
4. Variations give the organisms an individuality of their own. 
5. Without variation, there would be no science of heredity as all individuals of a race, would be 
identical in all aspects. 
 
 
Note: Mendel postulated laws of inheritance using Quantitative approach. 
In 1860s, Gregor Mendel formulated a theory of inheritance based on experiments with garden peas, proposing 
that parents pass on to their offspring discrete hereditary factors (now called genes or alleles) that retain their 
identity through generations. Note Mendel did not call them genes. Later in 1909 Danish botanist Wilhelm 
Johannsen named these presumed hereditary particles “genes.” 
 
 
Q5: Name the two laws of inheritance postulated by Mendel? 
 
Answer: 
1. The Law of Segregation 
2. The law of Independent Assortment 
 
Q6: How do Mendel’s experiments show that traits may be dominant or recessive? 
 
Answer: Mendel took one tall pea (TT) plant and one short pea (tt) plant and produced progeny from 
them. The plants grown from F1 seeds represent first filial (F1) generation. All F1 plants were tall. 
Then Mendel self-pollinated F1 plants and found that all plants obtained in F2 progeny were not tall. 
Instead 75% were tall (dominant) while remaining 25% were dwarf (recessive traits). 
From the experiment, he concluded the F1 progeny is not a true breed but carries both traits. He 
concluded one trait is dominant over the other, that's why plants appear tall. It is also called the law of 
Segregation. 
 
 
 
Q7: How do Mendel’s experiments show that traits are inherited independently? 
 
Answer: When a pea plant of round green (RRyy) seeds is crossed with a pea plant having wrinkled 
yellow seeds (rrYY), plants in F1 progeny have round and yellow seeds. However in F2 generation, all 
traits appear independently. In F2, he got the following result (called dihybrid ratio): 
Round Yellow - 9 
Round Green - 3 
Wrinkled Yellow - 3 
Wrinkled Green - 1 
He concluded alleles controlling different traits are not linked and are inherited independently. It is 
also known as Law of Independent Assortment. 
 
Q8(NCERT): 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? 
 
Answer: No the information does not suffice. The blood group is determined by a pair of genes. It 
might happen the gene responsible for O group in the daughter might be inherited from mother or 
from father. For example, one possibility is father having AO pair and mother has OO pair of genes. 
 
Q9: Define allelomorph. 
 
Answer: The contrasting pair of genes or alleles constitute an allelomorph. Examples : Tall and dwarf 
plants, wrinkled and smooth seed coat, white and violet coloured flower. 
 
Q10: What are different types of variations? 
 
Answer: There are two types: 
1. Somatic Variation - It pertains to body cells and it is not inherited. 
2. Germinal Variation - It pertains to germ cells or gametes and it is inheritable. It leads to speciation 
and evolution. 
 
 
Q11(CBSE exam): How one change adopted can perform different functions? 
 
Answer: The study of evolution reveals, one change occurred initially is used to perform other 
functions. For example, initially feathers were evolved for warmth, later they were adapted for flight. 
 
 
Q12: What do you mean by evolution? 
 
Answer: Evolution may be defined as a gradual development of more complex species from pre-
existing simpler forms. 
It is an extremely slow process and has occurred over millions of years,as revealed by fossil 
evidences. 
Evolution has thus resulted in the diversity of organisms, influenced by environmental selection. 
 
Q13(NCERT): How is the sex of the child determined in human beings? 
 
Answer: Normal human somatic cells are diploid. They have 46 chromosomes made up of two sets 
of23-one set from each parent. In human diploid cells, there are 22 homologous pairs of autosomes, 
each with a maternal and a paternal homolog. The 23rd pair, the sex chromosomes, determines 
whether the person is female (XX) or male (XY). 
 
Mother provides only X chromosomes. The sex of the child is determined by the type of chromosome 
(X or Y) received from male gamete. 
 
 
Q14(NCERT): What are the different ways in which individuals with a particular trait may increase 
in a population? 
 
Answer: 
1. Natural Selection: Certain variations give survival chances to individuals in a population in a 
changed situation resulting in increase of their population. 
2. Genetic drift: Accidents in small population even if they give no survival advantage, may lead to an 
increase of certain individuals in population. 
 
Q15: Why are traits acquired during the life-time of an individual not inherited? 
 
Answer: Any changes in somatic cells (or non-reproductive tissues) cannot be passed to DNA of germ 
cells. Hence these traits are not inheritable. 
 
 
Q16: Define Homozygous. 
 
Answer: An organism that has a pair of identical alleles for a character is said to be homozygous for 
the gene controlling that character.Homozygous plants "breed true" because all of their gametes 
contain the same allele- either TT or tt for example. 
 
 
Q17: Define Hetrozygous. 
 
Answer: An organism that has two different alleles for a gene is said to be heterozygous for that gene. 
Unlike homozygotes, heterozygotes are not true-breeding because they produce gametes with 
different alleles; for example Tt. 
 
Q18(NCERT): Why are the small numbers of surviving tigers a cause of worry from the point of 
view of genetics? 
 
Answer: Small number means fewer variations. It will affect the frequency of selection which is 
essential for survival. For effective selection, the population must consist of an infinitely large number 
of individuals in the population. For any reason, if these tigers die, chances of becoming extinct of 
these species are very high. 
 
 
Q19(NCERT): What factors could lead to the rise of a new species? 
 
Answer: 
i. Genetic Variation: Changes in gene frequency in small breeding isolated populations. 
ii. Natural selection 
iii. Genetic Drift. 
 
 
Q20(NCERT): Will geographical isolation be a major factor in the speciation of a self pollinating 
plant species? Why or why not? 
 
Answer: In this case geographical isolation does not become a major factor in the speciation of self 
pollinating plant. Since the plant is self pollinating, pollens can transfer to stigma of same flower or 
another flower of the same plant. 
 
Q21: Define Speciation. 
 
Answer: Speciation is arising of a new species from a sub-population of a species which is 
geographically or reproductively isolated over a long period of time from the other population of the 
same species. 
 
 
Q22(NCERT):Will geographical isolation be a major factor in the speciation of an organism that 
reproduces asexually? Why or why not? 
 
Answer: The answer can be either Yes or NO. 
Since the organism reproduces asexually, the offsprings are the identical DNA copies of their parent 
(variation is minimal in asexual reproduction). Geographical isolation alone, cannot be a major factor 
in the speciation of the organism. 
Geographical isolation can become a major contributing factor, if it increases the chance for a 
change to develop in their gene flow (Genetic drift), leading to formation of a new species. 
 
 
Q23: Who provided experimental evidence to support theory of origin of life from inanimate 
matter? 
 
Answer: Stanley L. Miller and Harold C. Urey in 1953. 
 
 
Q24: A normal pea plant bearing colored flowers suddenly start producing white flowers. What 
could be the possible cause? 
 
Page 5


    NCERT Solutions  
Heredity and evolution  
 
Ape man evolution 
 
 
Q1: Define Heredity. 
 
Answer: Heredity refers to the process by which certain features (heritable characteristics) are 
transmitted from parent to offspring. 
 
Q2: Define Variation. 
 
Answer: Offsprings of same parents do not exactly resemble each other as well as to their parents. It 
is known as variation. 
 
 
 
Q3(NCERT): 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. In asexual reproduction the traits which are present in previous generation are 
carried over to next generation with minor variations. Therefore the traits present in higher percentage 
have higher chances of persisting earlier.  
 
Q4(NCERT): How does the creation of variations in a species promote survival? 
 
Answer: Depending on the nature of variations different individuals would have different kinds of 
advantage e.g., Bacteria variants which can tolerate heat have better survival chances in heat wave in 
comparison to non-variant bacteria having no capacity to tolerate heat wave. 
However not all variations are useful or beneficial.  
Significance of Variation: 
1. It is the source of raw material for evolution. 
2. Animals are able to adapt themselves to the changing environment. 
3. Organisms are better suited to face the struggle for existence. 
4. Variations give the organisms an individuality of their own. 
5. Without variation, there would be no science of heredity as all individuals of a race, would be 
identical in all aspects. 
 
 
Note: Mendel postulated laws of inheritance using Quantitative approach. 
In 1860s, Gregor Mendel formulated a theory of inheritance based on experiments with garden peas, proposing 
that parents pass on to their offspring discrete hereditary factors (now called genes or alleles) that retain their 
identity through generations. Note Mendel did not call them genes. Later in 1909 Danish botanist Wilhelm 
Johannsen named these presumed hereditary particles “genes.” 
 
 
Q5: Name the two laws of inheritance postulated by Mendel? 
 
Answer: 
1. The Law of Segregation 
2. The law of Independent Assortment 
 
Q6: How do Mendel’s experiments show that traits may be dominant or recessive? 
 
Answer: Mendel took one tall pea (TT) plant and one short pea (tt) plant and produced progeny from 
them. The plants grown from F1 seeds represent first filial (F1) generation. All F1 plants were tall. 
Then Mendel self-pollinated F1 plants and found that all plants obtained in F2 progeny were not tall. 
Instead 75% were tall (dominant) while remaining 25% were dwarf (recessive traits). 
From the experiment, he concluded the F1 progeny is not a true breed but carries both traits. He 
concluded one trait is dominant over the other, that's why plants appear tall. It is also called the law of 
Segregation. 
 
 
 
Q7: How do Mendel’s experiments show that traits are inherited independently? 
 
Answer: When a pea plant of round green (RRyy) seeds is crossed with a pea plant having wrinkled 
yellow seeds (rrYY), plants in F1 progeny have round and yellow seeds. However in F2 generation, all 
traits appear independently. In F2, he got the following result (called dihybrid ratio): 
Round Yellow - 9 
Round Green - 3 
Wrinkled Yellow - 3 
Wrinkled Green - 1 
He concluded alleles controlling different traits are not linked and are inherited independently. It is 
also known as Law of Independent Assortment. 
 
Q8(NCERT): 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? 
 
Answer: No the information does not suffice. The blood group is determined by a pair of genes. It 
might happen the gene responsible for O group in the daughter might be inherited from mother or 
from father. For example, one possibility is father having AO pair and mother has OO pair of genes. 
 
Q9: Define allelomorph. 
 
Answer: The contrasting pair of genes or alleles constitute an allelomorph. Examples : Tall and dwarf 
plants, wrinkled and smooth seed coat, white and violet coloured flower. 
 
Q10: What are different types of variations? 
 
Answer: There are two types: 
1. Somatic Variation - It pertains to body cells and it is not inherited. 
2. Germinal Variation - It pertains to germ cells or gametes and it is inheritable. It leads to speciation 
and evolution. 
 
 
Q11(CBSE exam): How one change adopted can perform different functions? 
 
Answer: The study of evolution reveals, one change occurred initially is used to perform other 
functions. For example, initially feathers were evolved for warmth, later they were adapted for flight. 
 
 
Q12: What do you mean by evolution? 
 
Answer: Evolution may be defined as a gradual development of more complex species from pre-
existing simpler forms. 
It is an extremely slow process and has occurred over millions of years,as revealed by fossil 
evidences. 
Evolution has thus resulted in the diversity of organisms, influenced by environmental selection. 
 
Q13(NCERT): How is the sex of the child determined in human beings? 
 
Answer: Normal human somatic cells are diploid. They have 46 chromosomes made up of two sets 
of23-one set from each parent. In human diploid cells, there are 22 homologous pairs of autosomes, 
each with a maternal and a paternal homolog. The 23rd pair, the sex chromosomes, determines 
whether the person is female (XX) or male (XY). 
 
Mother provides only X chromosomes. The sex of the child is determined by the type of chromosome 
(X or Y) received from male gamete. 
 
 
Q14(NCERT): What are the different ways in which individuals with a particular trait may increase 
in a population? 
 
Answer: 
1. Natural Selection: Certain variations give survival chances to individuals in a population in a 
changed situation resulting in increase of their population. 
2. Genetic drift: Accidents in small population even if they give no survival advantage, may lead to an 
increase of certain individuals in population. 
 
Q15: Why are traits acquired during the life-time of an individual not inherited? 
 
Answer: Any changes in somatic cells (or non-reproductive tissues) cannot be passed to DNA of germ 
cells. Hence these traits are not inheritable. 
 
 
Q16: Define Homozygous. 
 
Answer: An organism that has a pair of identical alleles for a character is said to be homozygous for 
the gene controlling that character.Homozygous plants "breed true" because all of their gametes 
contain the same allele- either TT or tt for example. 
 
 
Q17: Define Hetrozygous. 
 
Answer: An organism that has two different alleles for a gene is said to be heterozygous for that gene. 
Unlike homozygotes, heterozygotes are not true-breeding because they produce gametes with 
different alleles; for example Tt. 
 
Q18(NCERT): Why are the small numbers of surviving tigers a cause of worry from the point of 
view of genetics? 
 
Answer: Small number means fewer variations. It will affect the frequency of selection which is 
essential for survival. For effective selection, the population must consist of an infinitely large number 
of individuals in the population. For any reason, if these tigers die, chances of becoming extinct of 
these species are very high. 
 
 
Q19(NCERT): What factors could lead to the rise of a new species? 
 
Answer: 
i. Genetic Variation: Changes in gene frequency in small breeding isolated populations. 
ii. Natural selection 
iii. Genetic Drift. 
 
 
Q20(NCERT): Will geographical isolation be a major factor in the speciation of a self pollinating 
plant species? Why or why not? 
 
Answer: In this case geographical isolation does not become a major factor in the speciation of self 
pollinating plant. Since the plant is self pollinating, pollens can transfer to stigma of same flower or 
another flower of the same plant. 
 
Q21: Define Speciation. 
 
Answer: Speciation is arising of a new species from a sub-population of a species which is 
geographically or reproductively isolated over a long period of time from the other population of the 
same species. 
 
 
Q22(NCERT):Will geographical isolation be a major factor in the speciation of an organism that 
reproduces asexually? Why or why not? 
 
Answer: The answer can be either Yes or NO. 
Since the organism reproduces asexually, the offsprings are the identical DNA copies of their parent 
(variation is minimal in asexual reproduction). Geographical isolation alone, cannot be a major factor 
in the speciation of the organism. 
Geographical isolation can become a major contributing factor, if it increases the chance for a 
change to develop in their gene flow (Genetic drift), leading to formation of a new species. 
 
 
Q23: Who provided experimental evidence to support theory of origin of life from inanimate 
matter? 
 
Answer: Stanley L. Miller and Harold C. Urey in 1953. 
 
 
Q24: A normal pea plant bearing colored flowers suddenly start producing white flowers. What 
could be the possible cause? 
 
Answer: Because of change in genetic sequence (called mutation). 
 
Q25: What is mutation? 
 
Answer: Organisms have evolved in number of ways to protect their DNA from changes. In spite of 
these mechanisms, however, changes in the DNA occasionally do occur. Any change in the DNA 
sequence is called a mutation. Mutations can be caused by errors in replication, transcription, cell 
division, or by external agents. E.g. nuclear radiation can lead to mutation. 
 
 
Q26: Give an example of characteristics being used to determine how close two species are in 
evolutionary terms. 
 
Answer: Analyzing the organ structure in fossils helps us to judge how far the evolutionary 
relationship goes, e.g., presence of feathers in some fossil dinosaurs indicate the birds are closely 
related to reptiles.  
Dinosaurs had feathers not for flying but instead these feathers provided insulation to keep warm their 
bodies. While the feathers in birds are used for flight. 
 
 
Q27: Can the wing of a butterfly and the wing of a bat be considered homologous organs? 
Why or why not? 
 
Answer: No, though the function of wings in both the cases is same but they are structurally different. 
And their origin is also different.They are analogous organs. 
 
 
Q28: What are fossils? What do they tell us about the process of evolution? 
 
Answer: A fossil is evidence of an organism that lived long ago. These are remnants or impressions of 
the extinct organisms which existed on earth millions of years ago. Fossils can be of following types: 
? Trace Fossils: These are indirect evidence of the dead organism. E.g. footprint, trail etc.  
? Casts: In rocks, the spaces are filled with dead organism making ts its replica or cast.  
? Molds: organism buried in sediment and decayed leaving an impression.  
? Petrified Fossils: minerals replacing the hard part of the organism  
? Frozen Fossils: Organism trapped in ice or in tree sap which hardened later.  
Fossils help us understand the process of evolution in following ways: 
1. These are the clues to the past, thus trace the path of evolution.  
2. Help in building evolutionary relationships among the present organisms. E.g. fossil evidence 
like Archaeopteryx and some characteristics of present-day birds like this hoatzin suggest 
that dinosaurs might have been the ancestors of today’s birds.  
3. Fossils help us in learning diversity of life and animal behaviour in past. This helped in 
understanding ancient environment and climate and categorizing geological time scale.  
 
Q29: 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: Although human beings look so different from each other in terms of size, colour and looks, 
but all of them belong to same species (Homo Sapiens) because of the following reasons: 
1. All human beings belong to same species and are able to interbreed.  
2. Fossil evidences prove that Archaic Homo sapiens arose in South Africa and moved across 
continents and developed into distinct races during the ice age.  
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