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Chapter 9

Heredity and Evolution

Intext Questions 

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.

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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 a few variants resistant to higher temperature 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 1:

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.

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.l3bVu6BzhYNdyriAE2SPHEyB1mafOae74udS ebAeV2yNnGpj3pgsKR94jrGjZ9WaF9My0X5XG7Rbo0p0d3tMmUQrUHMCcc3MKV8D0sfo671CA8Xb0jGGfWuq ko V4iPhRdgQudH3 aoQM2ShKK1hMiQWTKtBGTATMzqGantka77H9b8A2XxKMU0hQ7WUjKlOw2leVDY20C3jsss58t11tehmJg9La MpYamRAux1MXI4wzDaq6eD3rSU Yl9qHAuF4kDf4uBbbM

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 2:

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

Answer:

Mendel crossed pea plants having round green seeds (RRyy) with pea plants having wrinkled yellow seeds (rrYY).

An example of dihybrid crosses.
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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.

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Independent inheritance of two different traits

In the above cross, more than two factors are involved, and these are independently inherited.

Question 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 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 4:

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

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.

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Sex determination in humans

Question 1:

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:

  1. Natural selection: When that trait offers some survival advantage.
  2. Genetic drift: When some genes governing that trait become common in a population.
  3. When that trait gets acquired during the individual’s lifetime.

Question 2:

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

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 3:

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

Answer:

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 1:

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

Answer:

Natural selection, genetic drift and acquisition of traits during the lifetime of an individual can give rise to new species.

Question 2:

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

Answer:

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 3:

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 1:

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 2:

Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not?

Answer:

No, wing of bat and wings of butterfly should not be considered as homologous organs because they have different structure and origin but have the same function of flying so they are analogous organs.

Question 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 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.

Question 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:

A species is a group of organisms that are capable of interbreeding to produce fertile offspring. Skin colour, looks, and size are all a variety of features present in human beings. These features are generally environmentally controlled. Various human races are formed based on these features. However, there is no biological basis to this concept of races. Therefore, all human beings are a single species as humans of different colour, size, and looks are capable of reproduction and can produce a fertile offspring.

Question 2:

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

Answer:

Evolution cannot always be equated with progress or better body designs. Evolution simply creates more complex body designs. However, this does not mean that the simple body designs are inefficient. In fact, bacteria having a simple body design are still the most cosmopolitan organisms found on earth. They can survive hot springs, deep sea, and even freezing environments.

Therefore, bacteria, spiders, fish, and chimpanzees are all different branches of evolution.

Exercises

*Question 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

  1. TTWW
  2. TTww
  3. TtWW
  4. TtWw 

Answer:

(c) The genetic make-up of the tall parent can be depicted as TtWW

Since all the progeny bore violet flowers, it means that the tall plant having violet flowers has WW genotype for violet flower colour.

Since the progeny is both tall and short, the parent plant was not a pure tall plant. Its genotype must be Tt.

Question 2:

An example of homologous organs is

  1. our arm and a dog’s fore-leg.
  2. our teeth and an elephant’s tusks.
  3. potato and runners of grass.
  4. all of the above. 

Answer:

(b)An example of homologous organs is our teeth and an elephant’s tusks.

*Question 3:

In evolutionary terms, we have more in common with

  1. a Chinese school-boy.
  2. a chimpanzee.
  3. a spider.
  4. a bacterium. 

Answer:

(a) In evolutionary terms, we have more in common with a Chinese school boy.

*Question 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:

Let us assume that children with light-coloured eyes can either have LL or Ll or ll genotype. If the children have LL genotype, then their parents will also be of LL genotype.

LL × LL

LL

If the children with light-coloured eyes have ll genotype, then their parents will also have ll genotype.

ll × ll

ll

Therefore, it cannot be concluded whether light eye colour is dominant or recessive.

Question 5:

How are the areas of study − evolution and classification − interlinked? 

Answer:

Classification involves grouping of 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, then it means they have a more recent ancestor.

For example, in a family, a brother and sister are closely related and they have a recent common ancestor i.e., their parents. A brother and his cousin are also related but less than the sister and her brother. This is because the brother and his cousin have a common ancestor i.e., their grandparents in the second generation whereas the parents were from the first generation.

With subsequent generations, the variations make organisms more different than their ancestors.

This discussion clearly proves that we classify organisms according to their resemblance which is similar to creating an evolutionary tree.

*Question 6:

Explain the terms analogous and homologous organs with examples. 

Answer:

Homologous organs are similar in origin (or are embryologically similar) but perform different functions. For example, the forelimbs of humans and the wings of birds look different externally but their skeletal structure is similar. It means that their origin is similar (as wings in birds are modifications of the forearm) but functions are different – the wings help in flight whereas the human forearm helps in various activities.

      Homologous organs

Analogous organs, on the other hand, have different origin but perform similar functions. For example, the wings of a bird and a bat are similar in function but this similarity does not mean that these animals are more closely related. If we carefully look at these structures, then we will find that the wings of a bat are just the folds of skin that are stretched between its fingers whereas the wings of birds are present all along the arm. Therefore, these organs are analogous organs.

Question 7:

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

Answer:

Dogs have a variety of genes that govern coat colour. There are at least eleven identified gene series (A, B, C, D, E, F, G, M, P, S, T) that influence coat colour in dogs.

A dog inherits one gene from each of its parents. The dominant gene gets expressed in the phenotype. For example, in the B series, a dog can be genetically black or brown. Let us assume that one parent is homozygous black (BB), while the other parent is homozygous brown (bb)




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BB
BB
bBbBb
bBbBb

In this case, all the offsprings will be heterozygous (Bb).

Since black (B) is dominant, all the offsprings will be black. However, they will have both B and b alleles.

If such heterozygous pups are crossed, they will produce 25% homozygous black (BB), 50% heterozygous black (Bb), and 25% homozygous brown (bb) offsprings.

Bb
BBBBb
bBbbb

*Question 8:

Explain the importance of fossils in deciding evolutionary relationships.

Answer:

Fossils are the remains of the organism that once existed on earth. They represent the ancestors of the plants and animals that are alive today. They provide evidence of evolution by revealing the characteristics of the past organisms and the changes that have occurred in these organisms to give rise to the present organisms. Let us explain

the importance of fossils in deciding evolutionary history with the help of the following example.

Around 100 million years ago, some invertebrates died and were buried in the soil in that area. More sediment accumulated on top of it turning it into sedimentary rock.

At the same place, millions of years later, some dinosaurs died and their bodies were buried on top of the sedimentary rock. The mud containing dinosaurs also turned into a rock.

Then, millions of years later, some horse-like creatures died in that area and got fossilized in rocks above the dinosaur fossils.

Some time later, due to soil erosion or floods in that area, the rocks containing horse- like fossils are exposed.

If that area is excavated deeper, then the dinosaur and invertebrate fossils can also be found. Thus, by digging that area, scientists can easily predict that horse-like animals evolved later than the dinosaurs and the invertebrates.

Thus, the above example suggests that the fossils found closer to the surface of the earth are more recent ones than the fossils present in deeper layers.
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Layers of fossils:

Question 9:

What evidence do we have for the origin of life from inanimate matter? 

Answer:

A British scientist, J.B.S. Haldane suggested that life originated from simple inorganic molecules. He believed that when the earth was formed, it was a hot gaseous mass containing elements such as nitrogen, oxygen, carbon, hydrogen, etc. These elements combined to form molecules like water (H2O), carbon dioxide (CO2), methane (CH4), ammonia (NH3), etc.

After the formation of water, slowly the earth surface cooled and the inorganic molecules interacted with one another in water to form simple organic molecules such as sugars,fatty acids, amino acids, etc. The energy for these reactions was provided by solar radiations, lightning, volcanic eruptions, etc.

This was proved by the experiment of Stanley L. Miller and Harold C. Urey in 1953. They took a mixture of water (H2O), methane (CH4), ammonia (NH3), and hydrogen gas (H2) in a chamber and sparks were passed through this mixture using two electrodes.

After one week, 15% of the carbon from methane was converted into amino acids, sugars, etc. These organic molecules are polymerized and assembled to form protein molecules that gave rise to life on earth.

*Question 10:

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:

In sexual reproduction, two individuals having different variations combine their DNA to give rise to a new individual. Therefore, sexual reproduction allows more variations,

whereas in asexual reproduction, chance variations can only occur when the copying of DNA is not accurate.

Additionally, asexual reproduction allows very less variations because if there are more variations, then the resultant DNA will not be able to survive inside the inherited cellular apparatus.

However, in sexual reproduction, more variations are allowed and the resultant DNA is also able to survive, thus making the variations viable.

Variation and Evolution: Variants help the species to survive in all the conditions. Environmental conditions such as heat, light, pests, and food availability can change suddenly at only one place. At that time, only those variants resistant to these conditions would be able to survive. This will slowly lead to the evolution of a better adapted species. Thus, variation helps in the evolution of sexually reproducing organisms.

*Question 11:

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

Answer:

In human beings, every somatic cell of the body contains 23 pairs of chromosomes. Out of these 23 pairs, the first 22 pairs are known as autosomes and the remaining one pair is known as sex chromosomes represented as X and Y.

Females have two X chromosomes and males have one X and one Y chromosome. The gamete receives half of the chromosomes. Therefore, the male gametes have 22 autosomes and either X or Y chromosome.

The female gamete, on the other hand, has 22 autosomes and X chromosome.

During reproduction, the male and female gametes fuse and thus the progeny receives 22 autosomes and one X or Y chromosome from male parent and 22 autosomes and one X chromosome from the female parent.

Question 12:

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:

In species, variations that offer survival advantages are naturally selected. Individuals adjust to their environments with the help of these selected variations and consequently these variations are passed on to their progeny. Evolution of organisms occurs as a result of this natural selection.

However, there can be some other variations, which do not offer any survival advantage and arise only accidentally. Such variations in small populations can change the frequency of some genes even if they are not important for survival.

This accidental change in the frequency of genes in small populations is referred to as genetic drift.

Thus, genetic drift provides diversity (variations) without any survival advantage.

Access Answers of Science NCERT Class 10 Chapter 9 Heredity and Evolution (All In-text and Exercise Questions Solved)

Exercise-9.1 Page: 143

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?

Solution:

Trait B is more probable to arise early as this trait has already been existing and replicating in a larger percentage of the population as compared to trait A

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

Solution:

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.

Exercise-9.2 Page: 147

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

Solution:

Mendel showed that the traits can either be dominant or recessive through his experiments that focused on mono-hybrid cross. The experiment involved him crossing tall (TT) pea plants with dwarf (tt) pea plants. The resultant plants which formed after fertilization represented the F1 (or filial) generation. All the F1 plants were tall. Mendel then proceeded to self-pollinate the filial generation plants and the result was that 1/4th of the plants obtained in the F2 generation were dwarfs. From this experiment, Mendel concluded that the F1 tall plants were not true-breeding, instead they carried the traits for both tall and dwarf heights. A portion of the plants were tall due to the fact that the traits for tallness were dominant over the traits for dwarfness. This cements the notion that traits can either be dominant or recessive.

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

Solution:

Mendel’s experiments show that traits are inherited independently through his dihybrid cross experiment. The experiment involved him using two traits – namely, seed shape and seed colour. The colour yellow (YY) is dominant over green (yy), while the round shape (RR) is dominant over the wrinkled shape (rr). The F2 progeny of the dihybrid cross resulted in a phenotypic ratio of 9:3:3:1; therefore, 9 plants with round yellow (RRYY) seeds, 3 plants with round green (RRyy) seeds and 3 plants with wrinkled yellow (rrYY) seeds and one with wrinkled green seeds (rryy). He further observed that the wrinkled greens and the round yellow are parental combinations while the round green and wrinkled yellow are new. A dihybrid cross between two seeds with dominant traits (RRYY) and non-dominant traits (rryy) resulted in the production of 4 types of gametes (RY, Ry, rY and ry). This means each of the gametes segregate independently of the other; and each with a frequency of 25% of the total gametes produced.

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?

Solution:

Given information is not enough to tell us which characteristics are dominant –blood group A or O. Blood type A is always dominant in ABO blood and blood type O is always recessive. Here, the father’s blood group may be genotypically AA (homozygous) or AO (heterozygous), whereas that of mother can be OA or OO.

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

Solution:

Sex of child in humans is determined by the males. Males have XX chromosomes while females have XY chromosomes. Hence, if:

  • The male’s X chromosomes combines with the female’s X chromosomes, the mother gives birth to a girl
  • The male’s Y chromosome combines with the female’s X chromosome, the mother gives birth to a boy

Exercise-9.3 Page: 150

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

Solution:

An individual attribute could increase in a population within the following 2 ways:-

(a) Natural selection: if an attribute is useful to a population, it’ll increase naturally.

For example – mosquitoes which are resilient against a particular pesticide will pass on its genes, so that future generations become resistant as well. The mosquitoes which are affected by the pesticide die out.

(b) Genetic drift: if a species faces a catastrophic event where most of the population is wiped out, the surviving population can pass on their traits to the following generations. This may result in a rise of the attribute within the population.

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

Solution:

Traits acquired during a life-time cannot be inherited for successive generations as the changes do not reflect in the DNA of the germ cells. For instance, a football player cannot pass on his skills to his offspring as they are limited to non-reproductive cells only.

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

Solution:

As the size of the tiger population decreases, the genetic pool of the species decreases too. This results in a limitation on the variations which will be introduced within the genetic makeup of the tigers. This lack of variation will result in serious implications. For example, if an illness spreads within the tiger population, it can potentially wipe out the whole population, possibly causing their extinction.

Exercise-9.4 Page: 151

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

Solution:

Factors that would result in a new species are as follows:

(a) Mutation.

(b) Genetic drift.

(c) Natural selection.

(d) Geographical isolation.

(e) Generative isolation for prolonged periods

(f) Environmental factors on the isolated populations.

(g) Quantum of genetic variant transmissible from one generation to the following generation.

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

Solution:

In a pollination of plant species, geographical isolation is usually not a major factor as no new trait will become part of the genetic makeup in a self-pollinating plant species. However, there are some possibilities of some environmental changes which could result in some variations.

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

Solution:

In the case of asexually reproducing organisms, geographical isolation can’t be considered a factor. This is due to the fact that meiosis does not occur during asexual modes of reproduction.

Exercise-9.5 Page: 156

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

Solution:

Let us take the instance of humans and chimpanzees. Chimpanzees are able to express a wide range of emotions – such as busting out in laughter or smiling – this trait was once thought to be a feature exclusive to humans. The smile can be linked to the activation of the brain’s limbic system – where the orbicularis oculi muscle involuntarily contracts and raises the cheeks, forming wrinkles around the eyes. This implies that the smile is a true and genuine smile. Interestingly, this type of reflex has a name – the Duchenne smile. Moreover, research has shown that chimpanzees share 98.6% of our DNA – This means that humans and chimpanzees shared a common ancestor eons ago. It is important to also note that chimpanzees are the closest living relatives to humans.

2. Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not?

Solution:

The wing of a butterfly and the wing of a bat cannot be considered homologous organs as they do not share a common ancestor. Even though both structures aid in flying, they have evolved separately. To prove this, the wings of a butterfly are composed of two chitinous membranes, whereas wings of a bat are composed of bony skeleton, complete with blood vessels. Hence, these aren’t homologous organs but rather analogous organs.

3. What are fossils? What do they tell us about the process of evolution?

Solution:

Fossils are the preserved remains of animals or plants or other organisms that died out millions of years ago. These fossils tell us about a lot of extinct animals and also give insights into how evolution might have occurred. Fossils can be used to understand how an organism would have lived and what it may have looked like. More importantly, we can correlate with fossils as well as extant organisms to understand their relationships. For instance, scientists were able to recover protein sequences from a dinosaur called the T-rex, which confirmed its avian lineage. This means birds are the extant relatives of (avian) dinosaurs. Moreover, the pattern of fossil distribution gives us an idea of the time in history when various species were formed or become extinct.

Exercise-9.6 Page: 158

1. Why are human beings who look so different from each other in terms of size, color and looks said to belong to the same species?

Solution:

While human beings do vary in color and general appearance, their genetic makeup is identical to any other human. One of the speculations put forth for our drastic changes is due to evolutionary pressure – where the need to be easily recognized pushed us towards having widely different faces.

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

Solution:

Body designs are the result of environmental needs and pressure. Hence, we can’t conclude that one organism has a better body compared to another. For instance, fish have evolved a streamlined design as it is best suited for an aquatic environment. On the other hand, a spider or a chimpanzee might be ill-equipped to survive in such aquatic environments.

Exercises Page: 159

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

(a) TTWW

(b) TTww

(c) TtWW

(d) TtWw

Solution:

Correct answer – (c)

TtWW might be the genetic makeup of the tall parent. Since half the progenies are short, this implies that the parent plant also will have a collection of short genes; all progenies bore violet flowers, further suggesting that violet color is dominant over white.

2. An example of homologous organs is

(a) Our arm and a dog’s fore-leg.

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

(c) Potato and runners of grass.

(d) All of the above.

Solution:

Correct answer – (d)

Homologous organs have the same origin as each of the above organs, but different functions. Homologous organs can be defined as the organs of various animals having similar basic structure but different functions. For example, a whale’s flippers, a frog’s forelimbs, and man have the same basic structures but perform different functions, which is why they are called homologous organs.

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

(a) A Chinese school-boy.

(b) A chimpanzee.

(c) A spider.

(d) A bacterium.

Solution:

Correct answer – (a)

Humans and chimpanzees are related since they belong to the identical order (Primates) and same family, (Hominidae). However, a school-boy, regardless of the ethnicity is still a Homo sapien

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

Solution:

Knowledge of at least 3 generations is required for finding if an attribute is dominant or recessive. Hence, it is not possible to identify if the given trait is dominant or recessive.

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

Solution:

Classification and evolution are two related fields of biology. Evolution pertains to how organisms evolve and classification deals with finding out how two species are related to each other. For example, evolution and fossil evidence point to the fact that Australopithecus afarensis is considered one of our earliest ancestors. And classification tells us that Australopithecus afarensis belongs to the genus Homo, which is also the same genus as modern humans.

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

Solution:

Homologous organs are those organs that have the basic structural design as well as origin, however, serve different functions. For example: The forelimbs of humans and the wings of bats are anatomically similar.

Analogous organs are those organs that have a different structural design as well as origin, however perform similar functions. For example: The wings of birds and insects.

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

Solution:

Dogs have a certain set of genes that govern coat color. There are a minimum of eleven known sequence series (A, B, C, D, E, F, G, M, P, S, T) that influence the colour of a dog. A dog inherits one copy from each of its parents. As an example, within the B series, a dog is genetically black or brown. Assume that one parent is homozygous black (BB), whereas the other parent is homozygous brown (bb).

NCERT Solutions for Class 10 Chapter 9 Image 2

In this case, all the offsprings are going to be heterozygous (Bb).

Since black (B) is dominant, all the offsprings are going to be black. However, they are going to have each B and b alleles. If such heterozygous pups are crossed, they are going to produce 25 homozygous blacks (BB), 15 heterozygous black (Bb), and 25 homozygous brown (bb) offsprings.

NCERT Solutions for Class 10 Chapter 9 Image 3

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

Solution:

Fossils give evidence about:

(a) The organism and their paleobiology

(b) Even behaviour of an organism can be deduced to some extent (for example, paleontologists) had unearthed a site with more than 10,000 skeletons of a dinosaur called Hadrosaurus. This implies that the dinosaur lived in herds.

© Fossils also provide insight into the evolutionary history of animals and plants (for instance, paleontologists have discovered that whales had evolved from goat-sized land dwelling animal called Pakicetus)

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

Solution:

The evidence on the origin of life from inanimate matter was provided by Stanley L. Miller and Harold C. Urey’s experiment, which was conducted in 1953. They created an artificial environment which was reminiscent of the early earth’s atmosphere – it contained ammonia, hydrogen and other gases which were thought to have existed during primordial earth.

This concoction of gases was kept at a temperature slightly below 100 ° C. Additionally, sparks were generated to simulate lightning, which was also thought to be common during that period. At the end of the experiment, he was able to create 11 out of the 20 amino acids which is required for life.

10. 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?

Solution:

Sexual reproduction causes a lot of viable variations because of the following reasons:

(a) Error in copying of DNA (though it was rare)

(b) Random segregation of paternal and maternal chromosome at the time of sex cell formation.

(c) Exchange of genetic material between homologous chromosomes during the formation of gametes.

(d) Accumulation of variations occurred because of reproduction over generation after generation and choice naturally created wide diversity.

(e) In case of asexual reproduction, variation is severely limited as there is only one parent involved. Hence, the offspring is genetically similar to the parent

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

Solution:

Equal genetic contribution of male and female parents is ensured in progeny through the inheritance of equal numbers of chromosomes from both parents. There are 23 pairs of chromosomes but not all is paired. The 22 pairs are called autosomes while the remaining 1 pair is called the sex chromosomes (represented as X and Y.)

Females have two sets of X-chromosomes while males have 1 X-chromosome and 1 Y-chromosome.

During the process of reproduction, fertilization takes place, where the male gamete fuses with the female gamete and it results in the formation of a diploid zygote. Furthermore, the zygote receives an equal contribution of genetic material from both parents. The male contributes 22 autosomes plus, 1 X or Y chromosomes. The female contributes 22 autosomes, plus 1 X-chromosome.

12. 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?

Solution:

The statement holds true – only variations provide an advantage to individual organisms that will survive in a population. For example, variations that lead to the increase in heat-resistance in bacteria is very useful for survival if it finds itself in an environment where there is a sudden increase in ambient temperature. This will determine the difference between life and death for the bacteria.


NCERT Solutions for Class 10 Science Chapter 9 Heredity and Evolution

Chapter 9 – Heredity and Evolution are expected to have between 1 to 3 marks based on the yearly trends.

In 2018, however, only 1 question was asked (regarding Laws of Inheritance) in the Class 10 Science exam. But it would be wise to learn all the relevant concepts in order to avoid any unpleasant surprises.

The topics covered in this chapter are:

  • Laws of Inheritance
  • Mendel’s Experiments
  • Monohybrid cross
  • Dihybrid cross
  • Evolution and its theories
  • Evidence of evolution

NCERT Solutions for Class 10 Science Chapter 9 Heredity and Evolution

It is necessary to know how physical characteristics and traits are passed from a parent to his offspring. Furthermore, heredity provides a lot of insight into how genetics play a major role in organisms. Evolution is a gradual process where an organism changes and adapts to many variables. Sometimes, it is driven by the environment or competition.

Explore the definition of heredity and evolution. Discover its significance and implications. Find more learning resources on NCERT Solutions to aid your exam preparation and streamline your last-minute revisions.

Key Features of NCERT Solutions for Class 10 Science Chapter 9 Heredity and Evolution

  • Elaborate and detailed solutions
  • Tailored to meet CBSE prescribed norms
  • Use of simple and easy-to-understand language
  • Nearly all jargons are explained in detail
  • Access to a plethora of additional learning tools and resources ranging from sample papers to solved previous year question papers

Frequently Asked Questions on NCERT Solutions for Class 10 Science Chapter 9

What are analogous organs in the Chapter 9 of NCERT Solutions for Class 10 Science?

The organs of different species having similar functions are called analogous organs. The anatomical features of these organs might not be the same but the functions remain the same in all the organisms. Students can refer to the Chapter 9 of NCERT Solutions for Class 10 Science while answering the textbook questions to get a clear idea of the concepts. Both chapter wise and exercise wise solutions are available which can be used by the students based on their needs.


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NCERT Solutions Class 10 Science Chapters

  • Chapter 1 Chemical Reaction and equation
  • Chapter 2 Acid, Base and Salts
  • Chapter 3 Metals & Non-Metals
  • Chapter 4 Carbon and its Compounds
  • Chapter 5 Periodic Classification of Elements
  • Chapter 6 Life Processes
  • Chapter 7 Control and Coordination
  • Chapter 8 How do Organisms Reproduce
  • Chapter 9 Heridity
  • Chapter 10 Light, Reflection & Refraction
  • Chapter 11 Human Eye
  • Chapter 12 Electricity
  • Chapter 13 Magnetic effects of electric current
  • Chapter 14 Sources of Energy
  • Chapter 15 Environment

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