Principles of Genetics and Breeding

10.1.3 How are allele frequencies estimated?

When genotypes at a co-dominant locus are scored from a sample of individuals, the frequencies of the alleles at the locus can easily be calculated from these data. Remember that every individual has pairs of chromosomes, so they must also have pairs of alleles at each locus, that a homozygote at a locus has two of the same allele, and a heterozygote has two different alleles. Although a diploid individual can only exhibit two alleles at a locus, there may be many different alleles at the locus present in the population as a whole. Allele frequencies are the critical starting point for all further analyses of genetics in populations. By convention, the frequencies of alleles at a locus are symbolized using the lower-case letters p, q, r, s and the frequency of an allele is given by:

2H_o+H_e

P=------------------

2N

Where H_o = number of homozygotes for that allele, H_e = number of heterozygotes for the allele and N = number individuals scored at the locus.