CBSE Class 10 Science 2017 · Paper 31/1/C · Question 4

Speciation is the process by which a new species develops from an existing species: a population splits into groups that change until their members can no longer interbreed with each other. Two factors that could lead to speciation (any two): 1. Geographical isolation — a barrier such as a river or a mountain range divides a population, so little or no gene flow takes place between the two parts. 2. Genetic drift — random changes in the frequency of genes accumulate differently in the separated sub-populations over generations. (Also accepted: natural selection operating differently in the two places; severe changes in DNA, such as a change in the number of chromosomes, so that the germ cells of the two groups cannot fuse.)