9. Heredity and Evolution– Class 10 Science SEBA Assam Board
Chapter 9: Heredity and Evolution– SEBA/ASSEB Class 10 Science Textbook, Assam Board
Chapter 9: Heredity and Evolution
Internal Questions and Answers
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, which exists in 60% of the population, is likely to have arisen earlier. In asexually reproducing species, variations are passed to the next generation through reproduction. A trait present in a larger proportion of the population has had more time to spread and accumulate over generations. Hence, the trait with higher frequency is generally considered to have originated earlier.
2. How does the creation of variations in a species promote survival?
Answer: Variations help a species survive by increasing the chances that some individuals can adapt to changes in the environment. During unfavourable conditions such as diseases, climate changes or shortage of food, individuals with useful variations are more likely to survive and reproduce. These favourable traits are passed to the next generation, helping the species continue and evolve over time.
Internal Questions and Answers:
1. How do Mendel’s experiments show that traits may be dominant or recessive?
Answer: Mendel’s experiments with pea plants showed that when two contrasting traits were crossed, only one appeared in the first generation (
), while the other seemed to disappear. For example, when he crossed tall and dwarf plants, all plants were tall. However, in the next generation (
), both tall and dwarf plants reappeared in a 3:1 ratio. This showed that the trait expressed in the generation is dominant, while the hidden one is recessive but reappears in later generations.
2. How do Mendel’s experiments show that traits are inherited independently?
Answer: Mendel showed that traits are inherited independently through his dihybrid cross experiments. When he crossed pea plants differing in two traits (such as seed shape and seed colour), the F1 generation showed only the dominant traits. In the F2 generation, the traits reappeared in new combinations in a 9:3:3:1 ratio. This indicated that the inheritance of one trait does not affect the inheritance of another, proving that traits are passed independently of each other.
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 alone is not enough to tell which trait is dominant. The daughter has blood group O, which means she received one O allele from each parent. Therefore, the father with blood group A must have the genotype AO, while the mother has genotype OO. Since the father shows blood group A even with one A allele and one O allele, it shows that A is dominant over O.
4. How is the sex of the child determined in human beings?
Answer: In humans, the sex of a child is determined genetically. Women have two X chromosomes (XX), while men have one X and one Y chromosome (XY). Every child inherits an X chromosome from the mother, but the father can pass on either an X or a Y. If the child inherits the X from the father, it will be a girl; if it inherits the Y, it will be a boy. Thus, the father’s chromosome decides the child’s sex.
Internal Questions and Answers:
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 if the trait gives them a survival advantage and helps them reproduce more successfully. They may also increase due to genetic drift, where changes in gene frequency occur by chance, especially in small populations.
2. Why are traits acquired during the life-time of an individual not inherited?
Answer: Traits acquired during a person’s lifetime are not inherited because they do not cause any change in the genes present in the reproductive cells. These traits usually affect body cells only, like muscles developed by exercise or a scar from an injury. Since inheritance happens through genes in sperm and egg cells, only genetic changes can be passed to the next generation, not acquired traits.
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 serious concern from the genetics point of view because there is very less genetic variation left in the population. When the population size becomes very small, inbreeding increases, which can lead to genetic disorders and weak offspring. Due to low variation, tigers may not be able to adapt properly to diseases or environmental changes, which increases their risk of extinction.
Internal Questions and Answers:
1. What factors could lead to the rise of a new species ?
Answer: The factors that could lead to the formation of a new species are:
(i) Genetic drift: Changes in the frequency of genes in a population by chance.
(ii) Natural selection: Favourable variations help organisms survive and reproduce.
(iii) Geographical isolation: Physical barriers separate populations and prevent interbreeding.
2. Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?
Answer: Geographical isolation will not be a major factor in the speciation of a self-pollinating plant species. This is because such plants usually reproduce by pollinating themselves, so there is already very little exchange of genetic material with other plants. Even if they are separated by geographical barriers, it may not make much difference. Variation mainly arises due to mutations, not because of isolation.
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 may not be a major factor in the speciation of organisms that reproduce asexually. This is because they do not depend on mating for reproduction. However, geographical isolation can separate populations and prevent gene flow between them. Over many generations, variations and mutations may accumulate in these isolated populations, leading to the formation of new species.
Internal Questions and Answers:
1. Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Answer: An example is the presence of similar forelimb structure in different animals like humans, whales and bats. Though they perform different functions such as holding, swimming or flying, their basic bone arrangement is the same. Such homologous structures show that these species share a common ancestor. The more similar the characteristics, the more closely related the species are in evolutionary terms.
2. Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not?
Answer: No, the wing of a butterfly and the wing of a bat cannot be considered homologous organs. Although both are used for flying, their basic structure and origin are different. A butterfly’s wing is made of a thin membrane supported by veins and has no bones, while a bat’s wing has bones similar to the forelimbs of other mammals. So, they are analogous organs, not homologous.
3. What are fossils? What do they tell us about the process of evolution?
Answer: Fossils are the preserved remains, impressions or traces of ancient organisms found in rocks.
Fossils provide evidence for the process of evolution. They tell us about the organisms that lived in the past and how they have changed over time. By comparing fossils found in different rock layers, we can understand the evolutionary history of organisms. Fossils found in deeper rock layers are generally older than those found in upper layers. Thus, fossils help us trace the evolution of life on Earth .
Internal Questions and Answers:
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 may look different in size, skin colour or facial features, but all of them can interbreed with one another and produce fertile offspring. The basic body structure, genetic makeup and number of chromosomes are the same in all humans. These differences are mainly due to variations and environmental factors. Since they can reproduce among themselves, all humans belong to the same species.
2. In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design? Why or why not?
Answer: In evolutionary terms, we cannot say that one organism has a ‘better’ body design than the others. Bacteria, spiders, fish and chimpanzees are all well-adapted to their own environments. Evolution does not mean progress towards perfection, but adaptation for survival. Each organism has a body design that suits its lifestyle and surroundings. So, no species is superior; all are equally evolved in their own way.
Exercises of Chapter 9: Heredity and Evolution
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
Answer : (c) TtWW
[The given information indicates a typical Mendelian dihybrid cross involving two traits: plant height (tall or short) and flower color (violet or white). The fact that almost half of the progeny were short suggests that the tall parent must be heterozygous for the trait of plant height. The resulting progeny would have a genotype of Tt (heterozygous for height) and WW (heterozygous for flower color).]
Question : 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.
Answer : (d) all of the above.
[Homologous organs are organs that have a similar basic structure but may have different functions. ]
Question : In evolutionary terms, we have more in common with
(a) a Chinese school-boy. (b) a chimpanzee. (c) a spider. (d) a bacterium.
Answer: (a) A Chinese school-boy.
[ In evolutionary terms, we have more in common with a Chinese school-boy because both belong to the same species, Homo sapiens. We share almost all our genetic information and have a very recent common ancestry compared with chimpanzees, spiders and bacteria.]
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 determine whether light eye colour is dominant or recessive from this information alone. The fact that children with light-coloured eyes are likely to have parents with light-coloured eyes only shows that the trait may be inherited from their parents. To determine whether it is dominant or recessive, we need more information about the inheritance pattern of eye colour across different generations.
5. How are the areas of study – evolution and classification – interlinked?
Answer: Evolution and classification are interlinked because classification is based on the similarities and differences among organisms, which arise due to evolution. Organisms that share many similarities and have a common ancestor are placed in the same group. The more closely related organisms are, the more recent their common ancestor is likely to be. Thus, classification helps us understand the evolutionary relationships among organisms.
6. Explain the terms analogous and homologous organs with examples.
Answer: Homologous organs: Organs that have the same basic structure and origin but perform different functions are called homologous organs. Example: The forelimbs of humans, whales and bats.
Analogous organs: Organs that have different structures and origins but perform similar functions are called analogous organs. Example: The wings of birds and insects. Both help in flying, but their structures are different.
7. Outline a project which aims to find the dominant coat colour in dogs.
Answer: To find the dominant coat colour in dogs, we can carry out the following project:
Objective: To identify the dominant coat colour in dogs.
Method: Observe a large number of dogs and record their coat colours, such as black, brown and white. Then, study the coat colours of their parents and offspring.
Analysis: Compare the coat colours in different generations. If one coat colour appears more frequently in the offspring of dogs with contrasting coat colours, it may indicate dominance. However, frequency alone cannot prove that a colour is dominant.
Conclusion: Study the inheritance pattern over several generations to identify the dominant coat colour. Controlled breeding data and genetic analysis would help confirm the result.
8. Explain the importance of fossils in deciding evolutionary relationships.
Answer: Fossils help us to study the evolutionary relationships between different organisms. They provide evidence of the organisms that lived in the past. By comparing fossils with present-day organisms, we can understand how organisms have evolved over time. Fossils found in deeper rock layers are generally older than those found in upper layers. Thus, fossils help us trace the evolutionary history of organisms and understand their relationships with one another.
9. What evidence do we have for the origin of life from inanimate matter?
Answer: The evidence for the origin of life from inanimate matter is largely indirect and based on scientific theories and experiments. Key lines of evidence include laboratory simulations that demonstrate the synthesis of organic molecules under early Earth conditions, the presence of organic compounds in meteorites, and the identification of potential building blocks of life in various planetary environments.
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: Sexual reproduction gives rise to more viable variations than asexual reproduction through the process of recombination and genetic diversity. During sexual reproduction, genetic material from two parent organisms is combined, resulting in the shuffling and mixing of genetic traits. This generates new combinations of alleles and increases the genetic variability within a population.
The increased genetic diversity resulting from sexual reproduction enhances the adaptability and evolutionary potential of organisms. It provides a wider range of genetic variations for natural selection to act upon, allowing sexually reproducing organisms to adapt more effectively to changing environments and increasing their chances of long-term survival compared to asexual organisms with limited genetic variation.
11. 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 is ensured through sexual reproduction. During fertilization, the male gamete (sperm) fuses with the female gamete (egg) to form a zygote. Each gamete carries half of the genetic material of the parent, ensuring an equal contribution from both male and female parents to the genetic makeup of the progeny.
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: No, I do not agree with this statement. Only variations that provide an advantage do not necessarily survive in a population. Some variations may be neutral and have no effect on the survival of an organism. Their survival also depends on environmental conditions and the reproductive success of the organism. A variation that is advantageous in one environment may not be useful in another. Therefore, variations that confer an advantage are more likely to survive and be passed on to the next generation, but it is not necessary that only such variations will survive.
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