Assertion: hardy-weinberg principle explains the variations occuring in populatin and species over a number of generations.
Reason: Hardy-Weinberg principle is applicable only when genetic drift occurs.

Answer

D

Explanation

The relative frequencies of various kinds of genes in a large and randomly mating. Sexual panmictic population tend to remain constant from generation to generation in the absence of mutation, selection and gene flow. This is called Hardy-Weinberg principle or Hardy-Weinberg equilibrium. It is random in gene (allele) frequency and occurs only by chance it is non-directional. Genetic drift can cause elimination of certain alleles or fixation of the other in the population leading to a change in the populatin of alleles in the gene pool so, genetic drift must not occur to maintain the equilibrium.