Heredity and Evolution
NCERT Exercise Solution
Question 1: A Mendelian experiment consisted of breeding tall pea plant 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 makeup of the tall parent can be depicted as?
Answer: (c) TtWW
Question 2: An example of homologous organs is
- Our arm and a dog's fore-leg
- Our teeth and an elephant's tusks
- Potato and runners of a grass
- All of the above
Answer: (d) All of the above
Question 3: In evolutionary terms, we have more in common with
- A Chinese boy
- A chimpanzee
- A spider
- A bacterium
Answer: (a) A Chinese 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: This information is not sufficient. For considering a trait as dominant or recessive, we need data of at least three generations. This data is about only two generations.
Question 5: How are the areas of study, evolution and classification interlinked?
Answer: 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.
Question 6: Explain the term analogous and homologous organs with examples.
Answer: Homologous Organs: Organs which have common design but serve different functions in different animals are called homologous organs. For example; the forelimbs of all tetrapods are composed of humerus, radio-ulna, tarsals and metatarsals. Yet, the forelimbs of frogs are adapted to a jumping movement, those of birds are used for flying and those of humans are used for handling tools. This shows that frogs, birds and humans have evolved from a common ancestor.
Analogous Organs: Organs which have different design but serve a common function in different animals are called analogous organs. Wings of birds and wings of bat are good examples of a pair of analogous organs. Wings of birds are composed of all the bones of forelimb and are covered with feathers. Wings of bats are mainly composed of the digital bones and a thin membrane covering the structure. Yet wings in both the organisms are used for flying.
Question 7: Outline a project which aims to find the dominant coat colour in dogs.
Answer: For this, take a male dog with brown coat and bitch with white coat. Cross them to get the F1 generation. After that, allow the F2 generation to come into being. Tabulate data from two generations and find out the dominant coat colour.
Question 8: Explain the importance of fossils in deciding evolutionary relationships.
Answer: There are certain animals which became extinct millions of years ago. Fossils of many of such animals give important clues about missing links in the evolutionary relationship. The fossil of archaeopteryx is a good example of missing link. The fossil of archaeopteryx shows characters of birds and reptiles; which suggests that birds have evolved from reptiles. This example shows the importance of fossils in deciding evolutionary relationships.
Question 9: What evidence do we have for the origin of life from inanimate matter?
Answer: The famous experiment by Miller and Urey could establish that life originated from inanimate matter. These scientists replicated the conditions which may have existed during the early years of origin of the earth. In that experiment, inorganic substances gave rise to amino acids. Amino acid; we know are the bases of various biomolecules.
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: During sexual reproduction, genotype of the progeny is contributed by two different individuals. This opens up scope for various permutations and combinations. Moreover, the crossing over during meiosis is another means for producing variations. Hence, there are more chances of variations during sexual reproduction than during asexual reproduction.
Question 11: How is the equal genetic contribution of male and female parents ensured in the progeny?
Answer: Gametogenesis involves meiosis which leads to haploidy in the gametes. A zygote thus gets 50% of genes from each parent. Thus, equal genetic contribution is ensured from male and female parents.
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: This statement is true to some extent. There are many apparent variations which help an individual in survival. But there are certain variations which may not be beneficial, yet they are inherited through subsequent generations. The colourful plumage of peacock is a good example. The colourful plumage of a peacock helps it in finding a suitable mate but it also makes it conspicuous for its predators.