POPULATION GENETICS

It concerns the relative distribution of genes or inherited traits within a populations and the factors that change or maintain the frequency of genes or genotypes within it. The Hardy - Weinberg law is used to relate the frequencies of the genotypes at a single mendelian locus to the phenotype frequencies in that population. This law however is based on four assumptions.

1. There is no mutation occurring at the locus
2. There is no selection for any of the genotypes at the locus
3. Mating is completely random
4. There is no migration in to or out of the population.

In reality these assumptions are never entirely correct for any locus. If they are nearly correct, a locus is said to be in Hardy - Weinberg equilibrium.

The law states that, in a population at equilibrium, for a locus with two alleles D and d, having frequencies of p and q respectively, the genotype frequencies are :

DD = p2, Dd = 2pq and dd = q2

p + q = 1

(p + q)2 = p2 + 2pq + q2 = 1