Class 10 Science Chapter 9 Heredity and Evolution

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Class 10 Science Chapter 9 Heredity and Evolution

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Also, you can read the SCERT book online in these sections Solutions by Expert Teachers as per SCERT (CBSE) Book guidelines. These solutions are part of SCERT All Subject Solutions. Here we have given Assam Board Class 10 Science Chapter 9 Heredity and Evolution Solutions for All Subjects, You can practice these here.

Heredity and Evolution

Chapter – 9


Textual Questions and Answers:

 Page – 143 

Q.1. If a trait A exist 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: 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. 

Q.2. How does the creation of variations in a species promote its survival? 

Ans: Genetic variations enable the species to better adapt to changes in its environment. Moreover, it is an important force in evolution as it allows the frequency of alleles to increase or decrease through natural selection. These variations will determine the difference between extinction or continuation of the species.

Page – 147 

Q.1. How do Mendel’s experiments show that traits may be dominant or receive? 

Ans: Mendel’s experiments show that the Traits may be dominant or recessive by performing a monohybrid cross. Monohybrid cross between two pure breeding varieties always obtained hybrid progeny exhibiting one parental trait while the opposite trait was never expressed in the F1 generation. It suggested that two alleles of a gene are often either dominant or recessive and the presence of the dominant allele in F1 hybrids masks the expression of the recessive one.

Q.2. How do Mendel’s experiments show that traits are inherited independently? 

Ans: Mendel carried out dihybrid crosses by crossing two pea plants differing in contrasting traits of two characters. For example, he crossed a pea plant having yellow colour and round seed characters with another pea plant bearing green colour and wrinkled seed characters. In the F2 generation, he obtained pea plants with two parental and two recombinant phenotypes as yellow round and green wrinkled (parental) and yellow wrinkled and green round (recombinant). This indicated that traits separated from their original parental combinations and got inherited independently.

Q.3. A man with blood group A marries a women with the 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: No. This information is not sufficient to determine which of the traits – blood group A or O – is dominant. Thus is because we do not know about the blood group of all the progent. Blood group A can be genotypically AA of AO. Hence, the information is incomplete to draw any such conclusion.

Q.4. How is the sex of the child determined in human beings? 

Ans: Sex of a child depends on the chromosome in the gamete of the father. The unfertilized egg has one X chromosome. The sperm either has X chromosome or Y chromosome. If sperm carrying Y chromosome fertilizes with the egg, male child will be born with the genetic constitution XY. But if sperm carrying X chromosome fertilized with the egg, female child will be born with the genetic constitution XX. 

Page – 150

Q.1. What are the different ways in which individuals with a particular trait may increase in a population? 

Ans: An individual trait may increase in a population in the following ways:

1. Natural Selection: If a trait is useful to the population, it will increase naturally. It may directly lead to the evolution of species populations by adaptations to fit their environment better. That particular trait may thus increase in the population.

2. Genetic drift: If a population faces an accident such that the majority of its members get killed, the remaining members will pass on their traits to the subsequent generations. This leads to an increase of the trait in the population. This is the notion of genetic drift, which provides diversity without any adaptation.

3. Geographic isolation: Where a population of species gets separated by their respective group due to physical/natural barriers.

4. Mutation: Slight changes in the genetic information of the offspring during fertilization.

5. The trait is beneficial to the population: If a trait is beneficial to a population, it will increase naturally. Such green color in beetles is favorable as it helps them in camouflage against predators.

Q.2. Why are traits acquired during the life – time of an individual not inherited? 

Ans: For a trait of an organism to be inherited, it should being about a change in the genes present in the reproductive cells or gametes of that organism . The traits acquired during the life time of a person do not bring about a change in the genes present in its reproductive cells or gametes and hence they are not inherited by the offsprings. 

Q.3. Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics? 

Ans: A small number of surviving tiger are a cause of worry from the point of genetics because these tigers carry the genes which have made them adapt to the particular environment during the long process of evolution. If these tigers become extinct by some diseases or by hunting then the genes responsible for survival would also become extinct and would not be able to contribute in the survival of future generations.

Page – 151 

Q.1. What factors could lead to the rise of a new species? 

Ans: The main factors which lead to the rise of new species are natural selection, genetic drift, geographical isolation, and mutation. In speciation, a single evolutionary lineage gets split into two or more genetically independent lineages due to the actions of several environmental factors.


Q.1. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing with 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 for can be depicted as –

(a) TTWW 

(b) TTww 

(c) TtWW 

(d) TtWw 

Ans: (c) TtWW. 

Q.2. An example of homologous organs is 

(a) Our arm and a dog’s fore – leg. 

(b) Our teeth and an elephant’s tasks.

(c) Potato and runners of grass.

(d) All of the above.

Ans: (d) All of the above.

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

(a) A chinese school – boy 

(b) A chimpanzee.

(c) A spider.

(d) A bacterium. 

Ans: (a)  A chinese school – boy.

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

Ans: No because we cannot say with certainty whether light eye colour is dominant or recessive. However, since both children and their parents have light eye colour, the possibility that light eye colour is recessive trait.

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

Ans: Classification and evolution are highly interlinked fields of study. Classification is influenced by evolution. The modern system of classification is also called phylogenetic classification; which means it is based on evolutionary relationships. Hence, evolution and classification are closely related.

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

Ans: Homologous organs are those organs which have the same basic structural design and origin but have different functions.

For example: the forelimbs of humans and the wings of birds look different externally (morphologically dissimilar) but their skeletal structure is similar.

Analogous organs are those organs which have the different basic structural design and origin but have similar functions.

For example: the wings of birds and insects.

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

Ans: Cross the homozygous male BB and homozygous female bb, and then observe the coat colour in dog progeny (offspring). If all progeny have black colour, this means that black colour will be the dominant coat colour in dogs and if progeny will have brown colour then the brown colour will be dominant coat colour.

Q.8. Explain the importance of fossils in deciding evolutionary relationship.

Ans: Fossil provide us evidence about:

(i) The organisms that lived long ago such as the time period during which they lived, their structure etc.

(ii) Evolutionary development of species i.e., line of their development.

(iii) Connecting links between two groups. For example, feathers present in some dinosaurs means that birds are very closely related to reptiles.

(iv) Which organisms evolved earlier and which later.

(v) Development of complex body designs from the simple body designs.

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

Ans: Miller-Urey experiment provided evidence for the origin of life from inanimate matter. In the experiment, they created an atmosphere containing molecules like ammonia, methane and hydrogen sulphide, but no oxygen. This atmosphere was similar to the atmosphere present during the primitive Earth. Temperature was maintained constant at 100°C and sparks were passed through the mixture to stimulate lightning. After a particular time, certain amount of the carbon from methane had been converted to simple compounds of carbon like amino acids. Amino acids are the precursors of the proteins and proteins are the molecules that support the life in basic form.

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


  1. In asexual reproduction, there is no fusion of gametes, and only 1 parent is involved. So the only reason for variation is errors during DNA copying.
  2. These variations are very minute and can only be seen over a long period of time since too much deviation can lead to unsurvivable alterations in the genetic makeup for the progeny.
  3. Sexual reproduction gives rise to more viable variations than asexual reproduction because 2 gametes from different individuals combine to produce an organism. 
  4. It involves 2 parents so the offspring (child) shows variation due to the presence of characteristics of both parents.
  5. These variations help adapt to the environment in a better, more efficient manner , and result in evolution and formation of new species over time .

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

Ans: There are 23 pairs of chromosomes. Most human chromosomes have material and a paternal copy. We have 22 such pairs. These pairs contain half chromosomes from mother and half from father. One pair is called sex chromosomes. At the time of sex determination, the egg cell fuses with the sperm cell which are haploid to form zygote. Zygote is diploid which contains 23 chromosomes from mother and 23 from father. In this way, an equal genetic contribution of male and female parents is ensured in the progeny.

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

Ans: It is agreeable that only variations that confer an advantage to an individual organism will survive in a population. All variation does not necessarily provide an equal chance of survival to an organism in the environment. Survival chances highly depend on the nature of variations. For example- variation leading to the increase of heat-resistant bacteria is beneficial to the bacteria for its survival when it finds itself in a condition where suddenly there is an increase in the temperature of its habitat above the optimum temperature required for survival.

Multiple Choice Questions:

Q.1. The human species has genetic roots in: 

(a) America.

(b) Africa.

(c) Australia.

(d) Antarctica.

Ans: (b) Africa.

Q.2. Which of the following gas was not present in early earth atmosphere?  

(a) Ammonia.

(b) Oxygen.

(c) Hydrogen sulphide.

(d) Hethane.

Ans: (b) Oxygen.

Q.3. A gradual charge, over a long period, in a form of life in known as: 

(a) Erosion.

(b) Evolution.

(c) Revolution.

(d) Evaluation.

Ans: (b) Evolution.

Q.4. Scientists believe that all life originated in:

(a) The sea.

(b) The Soil.

(c) The ground.

(d) The air.

Ans: (a) The sea.

Q.5. According to scientists ares have evolved from: 

(a) Mammals.

(b) Amphibians.

(c) Reptiles.

(d) Arthropods.

Ans: (c) Reptiles.

Q.6. The theory of evolution of species by natural selection was given by 

(a) Mendel.

(b) Daruin.

(c) Palton.

(d) Lamark.

Ans: (b) Darwin.

Q.7. The term ‘ father of genetics ‘ is used for the scientists: 

(a) Morgan.

(b) Mendal.

(c) Darwin.

(d) Marie curie.

Ans: (b) Mendal.

Q.8. One of the following traits cannot be inherited. This one is: 

(a) Colour of eyes. 

(b) Colour of skin.

(c) Size of body.

(d) Nature of hair.

Ans: (c) Size of body.

Q.9. A zygote which has inherited an X chromosome from the father will develop into: 

(a) Baby boy.

(b) Baby girl.

(c) Adult.

(d) Either boy or girl.

Ans: (b) Baby girl.

Q.10. If the ratio of each phenotype of the seeds of pen plant in the F₂ generation is 9: 3: 3: 1, it is known as: 

(a) Tetrahybrid ratio.

(b) Monohybrid ratio.

(c) Dihybrid ratio.

(d) Trihybrid ratio.

Ans: (c) Dihybrid ratio.

Q.11. In evolutionary terms, we have more in common with:

(a) A chinese school boy.

(b) A chimpanzee.

(c) A spider.

(d) A bacterium.

Ans: (b) A chimpanzé.

Q.12. New species may be formed if: 

(i) DNA undergoes significant changes in germ cells.

(ii) Chromosome number changes in the gamete.

(iii) There is no change in the genetic material.

(iv) Mating does not take place.

(a) (i) and (ii) 

(b) (i) and (iii) 

(c) (ii), (iii) and (iv) 

(d) (i), (ii) and (iii) 

Ans: (a) (i) and (ii) 

Q.13. According to the evolutionary theory, formation of a new species in generally due to:

(a) Sudden creation by nature.

(b) Accumulation of variations over several generations.

(c) Clones formed during asexual reproduction.

(d) Movement of individuals from one habitat to another.

Ans: (b) Accumulation of variations over several generations.

Q.14. The presence of which of the following types of organs in two animals indicates that they are not derived from a common ancestor? 

(a) Homologous organs.

(b) Excretory organs.

(c) Analogous organs.

(d) Reproductive organs.

Ans: (c) Analogous organs.

Q.15. The presence of which of the following types of organs in two organisms indicates that they are derived from the same ancestor? 

(a) Analogous organs.

(b) Respiratory organs.

(c) Digestive organs.

(d) Homologous organs.

Ans: (d) Homologous organs.

Q.16. One of the following has not been produced from wild cabbage by the process of artificial selection. This one is

(a) Kohlrabi. 

(b) Cabbage. 

(c) Spinach.

(d) Kale.

Ans: (c) Spinach.

Q.17. The fossil trilobite was originally: 

(a) An arthropod.

(b) An invertebrate.

(c) A reptile.

(d) An ave.

Ans: (a) An arthropod.

Q.18. One pair of organs in the following animals are not homologous. This is: 

(a) Forelimbs in humans and lizard.

(b) Forelimbs in lizard and frog.

(c) Wings in butterfly and bat.

(d) Wings in bat and bird.

Ans: (c) Wings in butterfly and bat.

Q.19. The wings of a housefly and the wings of a sparrow are an example of: 

(a) Analogous organs.

(b) Vestigial organs.

(c) Respiratory organs.

(d) Homologous organs.

Ans: (a) Analogous organs.

Q.20. Select the group which shares the maximum number of common characters:

(a) Two individuals of a species.

(b) Two species of genus. 

(c) Two genera of a family.

(d) Two genera of two families.

Ans: (a) Two individuals of a species.

Q.21. The sex of a child is determined by which of the blw following?

(a) The length of the mother’s pregnancy. 

(b) The length of time between ovulation and copulation. 

(c) The presence of an X chromosome in an ovum. 

(d) The presence of a Y chromosome in a sperm.

Ans: (d) The presence of a Y chromosome in a sperm.

Q.22. Only one of the following characteristics of the parents can be inherited by their children. This one is: 

(a) Deep scar on chin. 

(b) Snub nose.

(c) Technique of swimming.

(d) Cut nose.

Ans: (b) Snub nose.

Q.23. The organs which perform different functions but have the same basic structure are known as: 

(a) Homologous organs.

(b) Analogous organs.

(c) Homolytic organs.

(d) Analytic organs.

Ans: (a) Homologous organs.

Q.24. The organs which perform similar functions but have different basic structure are called. 

(a) Asymmetric organs.

(b) Analogous organs.

(c) Homologous organs.

(d) Homophonic organ.

Ans: (b) Analogous organs.

Q.25. Wing of an insect and forelimb of a bird are: 

(a) Analogous organs.

(b) Analeptic organs.

(c) Homologous organs.

(d) Homophobic organs.

Ans: (a) Analogous organs.

Q.26. If the fossil of an organism is found in the deeper layers of earth, then we can predict that: 

(a) The extinction of organism has occured recently.

(b) The extinction of organism has occurred thousands of years ago. 

(c) The fossil position in the layers of earth in not related to its time of extinction.

(d) Time of extinction cannot be determined. 

Ans: (b) The extinction of organism has occurred thousands of years ago. 

Q.27. One of the following traits of the parents cannot be passed on to their future generations. This trait is:

(a) Cleft chain.

(b) pointed chin.

(c) Scarred chin.

(d) Broad chin.

Ans: (c) Scarred chin.

Q.28. Some dinosorous has feathers although they could not fly but birds have feathers that help them to fly. In the es context of evolution, this means that: 

(a) Reptiles have evolved from birds.

(b) There is no evolutionary connection between reptiles and birds.

(c) Birds have evolved from reptiles.

Ans: (c) Birds have evolved from reptiles.

Q.29. Select the incorrect statement from the following.

(a) Frequency of certain genes in a population changes over several generations resulting involution.

(b) Reduction in the weight of an organism due to starvation is genetically controlled.

(c) Low weight parents can have heavy weight progeny.

(d) Traits which are not inherited over generations do not cause evolution. 

Ans: (b) Reduction in the weight of an organism due to starvation is genetically controlled.

Q.30. When two parents are crossed , the offspring are referred to as: 

(a) Recessives. 

(b) Test cross. 

(c) F₁ generation. 

(d) F₂ generationen.

Ans: (c) F₁ generation. 

Q.31. A cross between two individuals results in a ratio of 9: 3: 3: 1 for four possible phenotypes of progeny. This is an example of a: 

(a) Dihybrid cross.

(b) Monohybrid cross.

(c) Test cross. 

(d) None of these.

Ans: (a) Dihybrid cross.

Q.32. For this experiments on heredity. Mendel used 

(a) Papaya plants.

(b) Potato plants.

(c) Pea plants.

(d) Pear plants. 

Ans: (c) Pea plants.

Q.33. The human animal which has an XY pair of chromosomes is called 

(a) Male.

(b) Hybrid.

(c) Female.

(d) doomed. 

Ans: (a) Male.

Q.34. The science of heredity is known as

(a) Biology.

(b) Embryology.

(c) Genetics. 

(d) Biochemistry. 

Ans: (c) Genetics.

Q.35. A gene is a:

(a) Hybrid. 

(b) Heritable trait.

(c) Pure breed

(d) Part of a chromosome that er lo sto sam quan do transmits a trait.

Ans: Part of a chromosome that er lo sto sam quan do transmits a trait.

Q.36. A normal cell of human body contain 23 pairs of chromosomes. The number of chromosomes in a sex cell ( sperm of ovum ) of a human being is most likely to be. 

(a) 46 

(b) 23 

(c) 21 

(d) 42 

Ans: (b) 23.

Q.37. In order to ensure that he had pure-breeding plants for his experiments, Mendel. 

(a) Cross fertilised each variety with each other.

(b) Let each variety self fertilise for several generations.

(c) Remove the female parts of the plants. 

(d) Removed the male parts of the plants. 

Ans: (b) Let each variety self fertilise for several generations.

Q.38. In the human blood grouping the four basic blood A, type B, type O. The blood proteins A and B are- 

(a) Simple dominant and recessive traits.

(b) Incomplete dominant traits.

(c) Codominant traits.

(d) Sex linked traits. 

Ans: (c) Codominant traits.

Q.39. A plant with ‘small’ genes breeds with a plant with two ‘tall’ genes to produce: 

(a) Small plants and tall plants in the ratio 1:3 

(b) All small plants.

(c) All tall plants.

(d) Tall plants and small plants in the ratio 3:1 

Ans: (c) All tall plants.

Q.40. A pregnant woman has an equal chance of her baby being blood group A or blood group AB. Which one of the following shows the possible genotypes of the woman and the father of her child? 

(a) lᴬIᴬ and IᴮIᵒ

(b) IᴬIᴮ and IᴮIᵒ

(c) IᴬIᵒ and IᴮIᵒ

(d) IᴬIᴮ and IᴬIᵒ

Ans: (a) lᴬIᴬ and IᴮIᵒ

Q.41. The palisade cells of a species of plant contain 28 chromosomes. How many chromosomes will there be in each gamete produced by the plant? 

(a) 56 

(b) 28

(c) 14 

(d) 4 

Ans: (c) 14 .

Q.42. Which of the following may be used to obtain on F₂ generation. 

(a) Allowing flowers on a parent plant to be self – pollinated.

(b) Allowing flowers on an F₁ plant to be self – pollinated. 

(c) Cross pollinating an F₁ plant with a parent plant.

(d) Cross pollinating two parent plants.

Ans: (b) Allowing flowers on an F₁ plant to be self – pollinated. 

Q.43. The visible characteristic in an organism is known as: 

(a) Prototype.

(b) Stereotype.

(c) Phenotype.

(d) Genotype.

Ans: (c) Phenotype.

Q.44. The exchange of genetic material takes place in: 

(a) Vegetative reproduction.

(b) A sexual reproduction.

(c) sexual reproduction.

(d) Budding.

Ans: (c) sexual reproduction.

Q.45. A cross between a tall plant (TT) and short plant (tt) resulted in progeny that were all tall plants because 

(a) Tallness is the dominant trait.

(b) Shortness is the dominant trait.

(c) Tallness is the recessive trait.

(d) Height of plant is not governed by gene T or t.

Ans: (a) Tallness is the dominant trait.

Q.46. The number of pair of sex chromosomes in the zygote of human is: 

(a) One.

(b) Two.

(c) Three.

(d) Four.

Ans: (a) One.

Q.47. In peas , a pure tall plant (TT) is crossed with a pure short plant (tt). The ratio of pure tall plants to pure short plants in F₂ generation will be: 

(a) 1:3 

(b) 3:1 

(c) 1:1 

(d) 2:1 

Ans: (c) 1:1

Q.48. The two variations of a trait which are brought in by the male and female gametes are situated on: 

(a) Copies of the same chromosome.

(b) Sex chromosomes.

(c) Two different chromosomes.

(d) Any chromosomes.

Ans: (a) Copies of the same chromosome.

Q.49. A trait in an organism is influenced by: 

(a) Paternal NDA only.

(b) Maternal DNA only.

(c) Both maternal and paternal DNA.

(d) Neither by paternal nor by maternal DNA 

Ans: (c) Both maternal and paternal DNA.

Q.50. In human males all the chromosomes are paired perfectly except one. This / these unpaired chromosomes in/are: 

(i) Large chromosome.

(ii) Small chromosome 

(iii) Y chromosome.

(iv) X chromosome.

(a) (i) and (ii) 

(b) (iii) only.

(c) (iii) and (iv) 

(d) (ii) and (iv) 

Ans: (c) (iii) and (iv) 

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