All the genes in a population at a given time is known as the gene pool. Over time the frequency of an allele in a population changes in response to a changing environment. The allele frequency can be calculated by simple formulae and the application of the Hardy-Weinberg PrincipleThe Hardy-Weinberg Principle states that in a stable population of diploid organisms with no disturbing factors, the allele frequencies will remain constant from one generation to the next.This assumes an isolated population with no migration, random mating and no selection pressures.