Heredity and Evolution: Science Class 10 Chapter 9 answers

mother, father, and baby, illustrating the chapter Heredity and Evolution of Class 10 science
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You will study heredity and evolution in Chapter 9 of Science Class 10 (NCERT, NBSE, SEBA, TBSE etc.) to better understand why children frequently resemble their parents. This is caused by the parent-transmitted DNA, which may have minute variations. The chapter also introduces Charles Darwin’s theory of evolution, which contends that all living things developed over millions of years through the process of natural selection. Get here the questions, answers, textbook solutions, PDF, MCQs of this chapter.

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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: Trait B is likely to have arisen earlier because in asexual reproduction, traits that are present in the previous generation are carried over to the next generation with minimal variations. Since trait B has a higher percentage in the population, it is more likely to have been present in the previous generation.

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

Answer: The creation of variations within a species, which can occur through sexual reproduction or due to inaccurate copying of DNA, can promote survival because different individuals may have different advantages depending on the nature of the variations. For example, bacteria with a variant that allows them to withstand heat may have a better chance of surviving a heat wave compared to non-variant bacteria that do not have the ability to tolerate heat. Overall, variations within a population of a species can help increase the chances of survival for the species as a whole.

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

Answer: In Mendel’s experiments, a trait that appeared in all members of the F1 generation and also in 75% of the F2 generation obtained by self-fertilization of the F1 generation is considered a dominant character. A trait that does not appear in the F generation but reappears in 25% of the F2 generation after self-fertilization of the F1 generation is considered a recessive trait.

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

Answer: Mendel crossed pure-breeding tall plants with round seeds with pure-breeding short plants with wrinkled seeds. The plants of the F1 generation were all tall with round seeds, indicating that the traits of tallness and round seeds were dominant. Self-breeding of the F1 generation yielded plants with the following characteristics: 9 tall and round-seeded, 3 tall and wrinkled-seeded, 3 short and round-seeded, and 1 short and wrinkled-seeded. The tall and wrinkled-seeded and short and round-seeded plants are new combinations that can only develop when the traits are inherited independently.

3. 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, this information is not sufficient to determine which of the traits – blood group A or O – is dominant. This is because we do not have information about the blood group of all the progeny. Blood group A can be genotypically AA or AO. Therefore, the information provided is incomplete and insufficient to draw any conclusions.

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

Answer: In human beings, females have two X chromosomes and males have one X and one Y chromosome. This means that females are XX and males are XY. Gametes receive half of the chromosomes, and male gametes have 22 autosomes and either an X or Y sex chromosome (22+X or 22+Y). Female gametes, on the other hand, only have an X sex chromosome (22+X) because females have XX sex chromosomes. The sex of the child is determined by the type of male gamete (X or Y) that fuses with the X chromosome of the female.

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

Answer: There are several ways in which individuals with a particular trait may increase in a population, including: natural selection, in which that trait offers some survival advantage; genetic drift, in which some genes governing that trait become common in a population; and the acquisition of a trait during the individual’s lifetime.

2. Why are traits acquired during the lifetime of an individual not inherited?

Answer: Traits that are acquired during an individual’s lifetime are not inherited because they involve changes in non-reproductive tissues, which cannot be passed on to germ cells or progeny. Therefore, these traits cannot be inherited.

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

Answer: The small number of surviving tigers is a cause of concern from a genetic perspective because it does not allow for a large amount of variation to occur, which is essential for the survival of the species. In addition, a deadly disease or calamity could potentially cause the death of all tigers. The small number of tigers also indicates that the existing tiger variants are not well adapted to the existing environment and may become extinct soon.

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

Answer: Natural selection, genetic drift, and the acquisition of traits during the lifetime of an individual can all contribute to the rise of a new species.

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

Answer: Geographical isolation may not be a major factor in the speciation of a self-pollinating plant species because self-pollination involves the transfer of pollen from the anther of one flower to the stigma of the same flower or another flower on the same plant. This means that geographical isolation would not prevent the transfer of pollen between plants.

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

Answer: No, geographical isolation is not likely to be a major factor in the speciation of an organism that reproduces asexually because asexual reproduction does not involve the exchange of genetic material between individuals. As a result, there is no opportunity for speciation to occur. However, geographical isolation can be a major factor in the speciation of cross-pollinated species because it can result in the separation of two populations, leading to the accumulation of variations in each population.

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

Answer: One example of characteristics being used to determine how close two species are in evolutionary terms is the presence of feathers in some ancient reptiles, such as dinosaurs. Fossil evidence suggests that these feathers evolved to provide insulation in cold weather, but were later adapted by birds for the purpose of flight. This indicates that birds are very closely related to reptiles, since dinosaurs were reptiles.

2. 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 not considered homologous organs because they perform similar functions (i.e., help the butterfly and the bat fly), but they are not believed to have evolved from a common ancestor. Instead, they are considered analogous organs because they serve similar purposes in unrelated species.

3. 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 provide evidence of the development of structures from simple to complex forms and can give us insight into the phases of evolution that these organisms may have undergone in order to survive in a competitive environment.

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1. 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: Human beings are considered to be part of the same species because they are capable of interbreeding to produce a fertile offspring. Despite differences in size, colour, and looks, human beings are still genetically similar and can produce a viable offspring. These differences in size, colour, and looks are due to a variety of genetic and environmental factors, and can lead to the development of different human races. However, all human races have enough similarities to be classified as the same species, as they are all capable of reproducing and producing a fertile offspring.

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

Answer: It is not accurate to say that any one of these groups has a “better” body design in evolutionary terms. Evolution does not always lead to the creation of more complex body designs, and it is not a measure of progress. Instead, it simply creates different body designs that are adapted to specific environments and needs. For example, bacteria have a simple body design, but they are able to survive in a wide range of environments, including hot springs, deep sea, and freezing temperatures. Therefore, all of these groups are different branches of evolution, and their body designs are adapted to their specific needs and environments.


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

Answer: (c) TtWW

2. An example of homologous organs is:

Answer: (b) our teeth and an elephant’s tusks.

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

Answer: (a) a Chinese school-boy.

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

Answer: No, we cannot say anything about whether the light eye colour trait is dominant or recessive based on this information. To determine whether a trait is dominant or recessive, data from at least three generations is needed. This data is only from two generations, so it is insufficient to make this determination.

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

Answer: Classification involves grouping organisms into a formal system based on similarities in internal and external structure or evolutionary history. Two species are more closely related if they have more characteristics in common, and if two species are more closely related, it means they have a more recent common ancestor. As subsequent generations evolve and accumulate variations, organisms become more different from their ancestors. This relationship between similarities and evolutionary history is what allows us to create an evolutionary tree and classify organisms according to their resemblance.

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

Answer: Homologous organs are those that have the same basic structural design and origin, but serve different functions. For example, the forelimbs of humans and the wings of birds have a similar skeletal structure, but they have different functions. Analogous organs are those that have a different basic structural design and origin, but serve a similar function. For example, the wings of birds and insects have different structural designs and origins, but they both serve the function of allowing the organism to fly.

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

Answer: To find the dominant coat colour in dogs, we could start by breeding two parents with known coat colours. For example, we could breed a homozygous black parent (BB) with a homozygous brown parent (bb). The resulting offspring will be heterozygous (Bb), and all of them will have a black coat due to the dominant black allele (B). If we then breed two of these heterozygous offspring (Bb), we would expect to get 25% homozygous black (BB) offspring, 50% heterozygous black (Bb) offspring, and 25% homozygous brown (bb) offspring. By continuing to breed these offspring and tracking the coat colours, we can determine which coat colour is dominant.

8. Explain the importance of fossils in deciding evolutionary relationships.

Answer: Fossils are important in determining evolutionary relationships because they provide evidence about the organisms that lived long ago, including the time period during which they lived and their structure. They also allow us to see the evolutionary development of species, and can provide connecting links between different groups of organisms. Fossils can also help us understand which organisms evolved earlier and which evolved later, and how complex body designs developed from simple body designs.

9. What evidence do we have that life may have originated from inanimate matter?

Answer: In 1953, Stanley L. Miller and Harold C. Urey conducted an experiment where they simulated an atmosphere similar to that thought to exist on early Earth, containing molecules like ammonia, methane, and hydrogen sulphide but no oxygen. They maintained the mixture at a temperature just below 100°C and used sparks to simulate lightning. After a week, they found that 15% of the carbon from methane had been converted to simple compounds of carbon, including amino acids which make up protein molecules and support life in its basic form. This suggests that life may have arisen anew on Earth.

10. A pea plant with blue flowers (BB) is crossbred with a pea plant with white flowers (ww):

(a) What is the expected color of the flowers in their F1 progeny?

(b) What will be the percentage of plants bearing white flowers in the F2 generation when the flowers of the F1 plants were selfed?

(c) State the expected ratio of the genotypes BB and Bw in the F2 progeny.


(a) Blue
(b) 25%
(c) BB:Bw = 1:2

11. List three main factors responsible for speciation and briefly describe each one.

Answer: Natural selection: This is the process by which organisms better adapted to their environment tend to survive and reproduce more.

Geographical barriers: These barriers, such as distance, mountains, and rivers, can separate the populations of a species. As a result, the populations may adapt differently to their environment, accumulate different variations, and become reproductively isolated, leading to the formation of a new species.

Genetic drift: This refers to random changes in the frequency of alleles in a gene pool, often occurring in small populations, regardless of whether they are beneficial or harmful.

12. Homologous organs are different from analogous organs. Mention the two basic characteristics that decide about analogy and homology between the two organs.

Answer: Homologous organs are different from analogous organs. The two main characteristics that distinguish between these two types of organs are:

  • Origin, structure, and function
  • Presence or absence of a true nucleus (only present in eukaryotic organisms)

13. Variation is useful for the survival of species over a long time. But the variants have unequal chances of survival. Explain this statement.

Answer: Variation is important for the survival of species over a long period of time, but not all variations are equally likely to survive. This is because variations often arise due to errors in DNA copying, and some of these variations may give the organism an advantage in its environment, increasing its chances of survival. For example, if a population of bacteria is exposed to higher temperatures, those that are tolerant to heat (variants) will survive while those that are not will die.

14. If a population of red beetles, living on green bushes is being eaten by crows. During sexual reproduction a green beetle is found in progeny:

(a) What is the future of this new trait?
(b) Will it survive in the new habitat?

Answer: If a population of red beetles living on green bushes is being eaten by crows, and during sexual reproduction a green beetle is found in the progeny:

(a) The green colored trait will become more common in the future

(b) It will have a better chance of survival because it will be harder for the crows to see it against the green bushes

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

Answer: Sexual reproduction gives rise to more viable variations than asexual reproduction because:

  • There are errors in DNA copying that can create new variations
  • Paternal and maternal chromosomes are randomly segregated during gamete formation
  • Genetic material is exchanged between homologous chromosomes during gamete formation
  • These variations accumulate over generations and are selected by nature, leading to a greater diversity of organisms

In contrast, asexual reproduction only allows for very small changes due to inaccuracies in DNA copying, so the offspring are generally more genetically similar to their parents. As a result, evolution tends to occur more quickly in sexually reproducing organisms compared to asexually reproducing organisms.

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

Answer: The equal genetic contribution of male and female parents in the progeny is ensured through the inheritance of an equal number of chromosomes from both parents. In humans, there are 23 pairs of chromosomes, with 22 pairs called autosomes and the remaining pair called sex chromosomes (represented as X and Y). Females have two X chromosomes and males have one X and one Y chromosome. During reproduction, the male gamete (haploid) fuses with the female gamete (haploid) to form the diploid zygote, which receives an equal contribution of genetic material from both parents. The male parent contributes 22 autosomes and one X or Y chromosome, while the female parent contributes 22 autosomes and one X chromosome.

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

Answer: Yes, we agree with this statement. Not all variations have an equal chance of survival in the environment in which they are found, as their chances of survival depend on the nature of the variations. For example, bacteria that can withstand higher temperatures will have a better chance of survival during a heat wave. The selection of variations by environmental factors forms the basis for the evolutionary process.

Tick (✓) the correct option

1. According to the evolutionary theory, formation of a new species is generally due to:

Answer: (b) accumulations of variations over several generations.

2. Select the correct statement:

Answer: (d) Wings of birds and wings of bat are homologous. Since they have same basic design however their origin is different.

 3. A zygote which has an X-chromosome inherited from the father will develop into a:

Answer: (b) girl

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

Answer: (c) 1:1

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