CBSE Class 10 Science 2020 · Paper 31/4/3 · Question 20(a)

Variation is the occurrence of differences in characters (structure and function) among the individuals of the same species, including the differences between offspring and their parents. Variation is beneficial to a species because it helps the species survive a change in its environment: when conditions change, for example when the water in which bacteria live becomes too hot, most individuals may die, but the variants suited to the new conditions survive and reproduce, so the species is not wiped out. Variation is also the basis of adaptation and evolution. Two reasons for variations among the progeny of sexual reproduction: (i) small errors (inaccuracies) in copying the DNA when germ cells are formed; (ii) the combination of DNA from two different parents at fertilisation, which gives each offspring a new combination of characters. Mutations (changes in DNA) are also accepted as a reason.