CBSE Class 10 Science 2020 · Paper 31/1/2 · Question 28

(a) Genetics is the study of heredity and variation. (b) Genes are segments of DNA that carry the information for traits (for making particular proteins) from one generation to the next. They are located on the chromosomes, in the nucleus of the cell. (c) (i) Natural selection: individuals whose variations suit the environment survive and reproduce more, so over generations these variations accumulate and can give rise to a new species. (ii) Genetic drift: random change in the frequency of genes in a small population over successive generations. (iii) Reproductive isolation: members of a group separated by a barrier (for example geographical) can no longer mate with the rest of the species, so their differences accumulate into a new species. Other correct factors, such as a large change in DNA, also earn credit.