The Hardy-Weinberg principle demonstrates a population which is set at genetic equilibrium. Genetic equilibrium is only established when the genotype and allele frequencies do not change at all over the course of generations. A common misconception is that the dominant allele is always more common than the recessive, which is not entirely true. When the population is large, as stated in the Hardy-Weinberg principle, inheritance does not cause changes in allele frequencies. The five conditions that must be maintained in order to maintain genetic equilibrium are: random mating, no net mutations, large population size, no migration, and no natural selection.

If there is random mating present, then each individual comprised within a population has an equal chance of mating with any other individual in that population of the opposite gender. There cannot be mutations because that would alter the frequencies and would change the population. Large population size is essential to this principle because only in small populations can genetic drift alter the allele frequencies. If there were no migration that means alleles would not be exchanged with other populations. Lastly, no natural selection is obvious because that would mean only certain genotypes and phenotypes are favored over others. This would prompt a change in allele frequencies which can disrupt the genetic equilibrium. This is demonstrated in the equations: p + q=1, and p2 + 2pq + q2 =1. The first equation is for the allele frequencies, while the second equations refer to the genotype frequencies. This principle allows a population’s genotype, phenotype, and allele frequencies to be calculated.

external image 180px-Wilhelm_Weinberg.jpg
external image hardy_eq.GIF