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HEREDITY AND EVOLUTION . What is a gene? Answer. Gene is the unit of inheritance. Gene is the part of a chromosome which controls the appearance of a set of hereditary characteristics. What is meant by analogous organs? Taking a suitable example o O a common function of flying but their origins a are not common. So, birds and bats au are ot closely related. . What is a sex chromosome? Answer. Sex chromosome is a chromosome that operates in the sex-determining mechanism of a species. Many animals have two different types of sex chromosomes. For example, in human there is a large X chromosome and a much smaller Y chromosome. Define ‘evolution’. Describe Darwin's theory of evolution. Answer. Evolution is the sequence of gradual changes which take place in the primitive organisms over millions of years and new species are produced. Since, the evolution is of the living organisms, so it is called ‘Organic Evolution’. Darwin's theory of Evolution: Charles Robert Darwin gave the theory of evolution in his famous book, ‘The Origin of Species’. The theory of evolution proposed by Darwin is known as ‘The Theory of Natural Selection’. It is also called ‘Darwinism’. According to Darwin's theory of evolution: a) There is natural variation within any population and some individuals have more favourable variations than others. b) Population remains fairly constant even though all species produce a large number of off springs. c) This i; due to ‘competition’ or struggle for existence between same and different species. d) The struggle for survival within population eliminates the unfit individuals and those with ‘favourable variations’ survive and pass on these variations to their progeny to continue. This is called natural selection. e) The favourable variations are accumulated over a long time period leading to the origin of a new species. “The sex of the children is determined by what they inherit from their father and not their mother.” Justify. Answer. It is because a child who inherits an X chromosome from her father will be a girl and one who inherits a Y chromosome from his father will be a boy. But all children inherit a X chromosome from their mother regardless of whether they are boys or girls. . Define variation in relation to a species. Why is variation beneficial to the species? Answer. Variation refers to the differences in the characters or traits among the individuals of a species. Variations are beneficial to the species because: a) They enable the organisms to adapt themselves in changing environment. b) Variations form the basis of heredity. c) They form the raw materials for evolution and development of new species. Describe briefly four ways in which individuals with a particular trait may increase in a population. Answer, The four ways in which individuals with a particular trait may increase in a population are as follows: a) Sexual reproduction results into variations. b) The individuals with special traits survive the attack of their predators and multiply while the other will perish. 2) Canntic drift nreiidac dieeciter ithaut nev ndantation Scanned with CamScanner 
