Genetic equilibrium occurs when allele frequencies at a locus are not changing and therefore the
population is not evolving. Allele frequencies change when a population is evolving.
The Hardy-Weinberg formula is used to establish allele frequencies at genetic equilibrium (no
evolution), which is possible under these conditions:
No mutations are occurring.
The population is very, very large.
The population is isolated from other populations of the same species (no immigration or
emigration).
All members survive and reproduce (no selection).
Mating is completely random.
Because these five conditions are not fulfilled in natural populations, any deviation from the
reference point established by the "rule" will indicate evolution.
The Hardy-Weinberg formula
At genetic equilibrium, proportions of genotypes at a locus with two alleles are given by the
equation:
