Allele frequency refers to how common an allele is in a population. It is determined by counting how many times the allele appears in the population then dividing by the total number of copies of the gene.
For instance, if all the alleles in a population of pea plants were purple alleles, W, the allele frequency of W would be 100%, or 1.0. However, if half the alleles were W and half were w, each allele would have an allele frequency of 50%, or 0.5.
Formula:
Frequency of allele A = Ac ÷ Aa
Where,Ac = Number of copies of allele A in population
Aa = Total number of copies of gene in population