Anyone outside of UT Martin wishing to use these notes or to contact me for additional information should first read the information obtained by clicking here . Suppose that they are diploid, and reproduce sexually. Consider one gene with two alleles, A and a. The possible genotypes are therefore AA, Aa, and aa.
First lets define the allele frequencies mathematically.
We could determine th e allele frequency of allele A and the allele frequency of allele a. To do this, we would count all the alleles in the population, and determine the proportion of them that are A and the proportion of them that are a. Note also that allele frequencies are proportions. We could determine genotype frequencies for AA, Aa and aa by counting up all individuals with each genotype in the population and then determining the proportion of all the individuals that are AA, the proportion that are Aa, and the proportion that are aa. The formulas given above are simply definitions of allele and genotype frequencies.