The Hardy-Weinberg principle states that both allele and genotype frequencies in a population will remain in an equilibrium from one generation to the next unless a disturbing influenced is introduced. However, in natural settings, many disturbances can occur. These can include mutations, non-random mating and selection among others. The frequencies of genotypes based on this principle occurring in nature is impossible because migration can occur within a population, taking away some members of the gene pool and sometimes, emigration into a population can occur, introducing new alleles. The alleles always have a chance of mutating and sometimes, there may be natural selection occurring favoring one allele over another in a particular environment. Therefore, although this principle states, in a simple two gene situation with A and a that the results should be frequency of AA=p2(squared) and the frequency of Aa should be 2pq and the frequency of aa should be q2(squared), you will not get those results outside a controlled laboratory setting.