Hardy Weinberg equation gives the relationship between allelic and genotypi frequencies in a population.
p is the probability of the dominant allele and q is that of the recessive allele for a particular trait controlled by 2 allels A and a.
i.e p is all of alleles in individuals with homozygous dominant genotype(AA) and half of individuals with heterozygous genotype(Aa).
like wise for q.
p=AA+1/2Aa q=aa+1/2Aa
Since there are only 2 alleles here, p+q = 1.
hence the chances of all possible alleles occuring randomnly
(p+q)^2 ( p+q whole square) = 1
p^2 +2pq + q^2 =1.
where p^2 is the predicted frequency of homozygous dominant individuals(AA)
2pq is the predicted frequency of heterozygous individuals.(Aa)
q^2 is the predicted frequency of homozygous reessiev individuals.(aa)
This can also be derived by using Punnett square.
female
A (p) a(q)
male A(p) p^2 pq
a(q) pq q^2
