Editing Allele (section)

==Genotype frequencies==
{{main|Allele frequency}}
The frequency of alleles in a diploid population can be used to predict the frequencies of the corresponding genotypes (see [[Hardy–Weinberg principle]]). For a simple model, with two alleles;

: <math>p + q=1 \, </math>

: <math>p^2 + 2pq + q^2=1 \,</math>

where ''p'' is the frequency of one allele and ''q'' is the frequency of the alternative allele, which necessarily sum to unity. Then, ''p''<sup>2</sup> is the fraction of the population homozygous for the first allele, 2''pq'' is the fraction of heterozygotes, and ''q''<sup>2</sup> is the fraction homozygous for the alternative allele. If the first allele is dominant to the second then the fraction of the population that will show the dominant phenotype is ''p''<sup>2</sup> + 2''pq'', and the fraction with the recessive phenotype is ''q''<sup>2</sup>.

With three alleles:

: <math>p + q + r = 1 \, </math> and

: <math>p^2 + q^2 + r^2 + 2pq + 2pr + 2qr = 1. \,</math>

In the case of multiple alleles at a diploid locus, the number of possible genotypes (G) with a number of alleles (a) is given by the expression:

: <math>G= \frac{a(a+1)}{2}. </math>