Hardy-Weinberg

The Hardy-Weinberg Theorem states that the allele frequencies of a gene in a population will remain constant, as long as evolutionary forces are not acting. H-W therefore provides a baseline (a null expectation) for a population that is not evolving. For a population to be in H-W equilibrium, the following conditions or assumptions must be met:

1. The population is very large; there is no genetic drift
2. Matings are random
3. There is no mutation
4. There is no migration
5. There is no selection

If one of these conditions is broken, an evolutionary force is acting to change allele frequencies, and the population may not be in H-W equilibrium. Natural populations probably seldom meet all of these conditions; H-W provides a nice model to study evolution via deviations from H-W equilibrium.

Hardy Weinberg Equation

Basic Relations

A = dominant allele
a = recessive allele

p + q = 1
Where p = frequency of A allele
q = frequency of a allele

p2 + 2pq + q2 = 1
Where p2 = frequency of AA genotype
2pq = frequency of Aa genotype
q2 = frequency of aa genotype