Heredity and Evolution (Question Answer)

QUESTIONS

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: B trait has arisen earlier because it exists in maximum population.

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

Answer: The variations created in a species protects the organism from extinction even in adverse conditions. As a result, the organism gains stability. Helps to adapt to the changing environment of the natural environment.

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

Answer: Mendel used a number of contrasting visible characters of garden peas – round/wrinkled seeds, tall/short plants, white/violet flowers and so on. He took pea plants with different characteristics – a tall plant and a short plant, produced progeny from them, and calculated the percentages of tall or short progeny.

                    In the first place, there were no halfway characteristics in this first generation, or F1 progeny – no ‘medium-height’ plants. All plants were tall. This meant that only one of the parental traits was seen, not some mixture of the two.  Mendelian experiments test this by getting both the parental plants and these F1 tall plants to reproduce by self-pollination. The progeny of the parental plants are, of course, all tall. However, the second-generation, or F2, progeny of the F1 tall plants are not all tall. Instead, one quarter of them are short. This indicates that both the tallness and shortness traits were inherited in the F1 plants, but only the tallness trait was expressed. Based on these tests, first-generation traits are dominant and traits that have not been revealed are recessive.

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

Answer: Mendel used a number of contrasting visible characters of garden peas – round/wrinkled seeds, tall/short plants, white/violet flowers and so on. He took pea plants with different characteristics – a tall plant and a short plant, produced progeny from them, and calculated the percentages of tall or short progeny. In the first place, there were no halfway characteristics in this first generation, or F1 progeny – no ‘medium-height’ plants. All plants were tall. This meant that only one of the parental traits was seen, not some mixture of the two. Mendelian experiments test this by getting both the parental plants and these F1 tall plants to reproduce by self-pollination. The progeny of the parental plants are, of course, all tall. However, the second-generation, or F2, progeny of the F1 tall plants are not all tall. Instead, one quarter of them are short. This indicates that both the tallness and shortness traits were inherited in the F1 plants, but only the tallness trait was expressed. Thus, two copies of the trait are inherited in each sexually reproducing organism. These two may be identical, or may be different, depending on the parentage.

5. 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: This information is not enough. Because each person carries two characters. Dominant characters can only appear when the characters are the same. If A group is dominant and O group is recessive then group O of a girl's blood can only occur when the two dominant characters are together in the body of the mother's and has the character of an O and an A in the father's body.

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

Answer: In the case of human beings, 22 pairs of chromosomes are carried by the child which come from the father and mother. In addition, there is one pair of sex chromosome in human. In the case of females, this sex-determining chromosome stay in pair of and called the X chromosome. However, in the case of males, the sex-determining chromosomes do not matched properly.  Therefore, in the case of females, the sex chromosome is XX and in males it is XY.

        For both boys and girl's one X chromosome is always from the mother's side. Therefore, the sex of the child is determined on the basis of the flow of the sex chromosome from the father's side. If in the case of infants, one X chromosome flows from the father's side and the one X chromosome flows from the mother's side then the child will be a girl.. If one X chromosome flows from the mother's side and Y chromosome flows flow from the father's side then the child will be a boy.

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

Answer: Different ways in which individuals with a particular trait may increase in a population are-

                 (1) Natural selection: Natural selection allows a living population to survive in the environment.

                 (2) Genetic drift: Changes in the genetic makeup contribute to the emergence of new species.

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

Answer: The traits acquired by an organism during its lifetime are not passed on to its offspring because these traits are not stored in the DNA of the organism and therefore cannot make change in the DNA of the germ cell.

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

Answer: From a genetic point of view, the declining number of living tigers is a matter of concern because of the negligible genetic pathways in tigers. Therefore, rapid environmental changes may not be favorable for them. If these changes are not controlled, the tigers will become extinct.

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

Answer: The following factors contribute to the origin of a new species ---

                (1) Variation: Diversity created in a species gives an organism a chance to survive and helps in the emergence of a new species.

                (2) Genetic drift: Changes in the genetic makeup contribute to the emergence of new species.

                (3) Geographical isolation: Nationalization will take place only when it is geographically segregated along with the differences.

11. 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 cause of speciation for self-pollinated plant species as self-pollinated plants do not depend on other plants for pollination and fertilization. Since self-pollination occurs within the same plant, geographical isolation cannot be a major cause of speciation in such plants.

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

Answer: Geographical isolation will not be a major factor in the speciation of an organism that reproduce asexually, because asexual reproduction does not require two organisms.

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

Answer: If the same characteristics are displayed in different organisms, then those organisms are considered to be of the same species. For example, there is a resemblance between a wings of a bat and a bird. Therefore, they can be said to be closely related. However, there is no wings in lizard and squirrel, hence they are not related to birds or bats.

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

Answer: Wing of a butterfly and wing of a bat cannot be considered as homologous organs. Although they looks identical and they perform the same function, but their origins are different.

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

Answer: A fossil is the hard remains of a prehistoric animal or plant that are found inside a rock. When an organism dies, its body is decomposed. But sometimes some parts of an organism do not decompose completely in the environment. For example, if a dead bird is sometimes exposed to hot lava, its body does not decompose easily, the lava becomes hard and leaves an insect mark. Such remnants are called fossils.

                Fossils provide the following information about the process of evolution:

1. It gives an idea of ​​the changes that are taking place on the surface of the earth and the animals that are associated with it.

2. Fossils provide information on the continuous evolution of less developed simple organisms to more advanced organisms.

3. They give evidence of the evolutionary process of human beings.

16. 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: Due to the different genetic makeup of human beings, their shape, color and shape are different. But they have no reproductive isolation. Reproductive isolation sets one species apart from other species. Therefore, they are different in shape, color and shape even though they belong to the same species.

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

Answer: Bacteria are primitive organisms because they existed in the very early stages of evolution. But they are still alive today, millions of years later. This is because they have adapted well to the changing environment over the years. Like spiders, fish and chimpanzees, living things have adapted to the changing environment and survived. Therefore, all these organisms have a very high level of body evolution.

EXERCISES

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 

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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 

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

(a) a Chinese school-boy

 (b) a chimpanzee 

(c) a spider 

(d) a bacterium 

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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? 

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

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

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

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

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

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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? 

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

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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?

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