p stands for: c. the dominant allele
q therefore stands for the recessive allele. The frequency of the homozygous dominant genotype (i.e. gene T is TT), so p×p, which = p^2
The frequency of the homozygous recessive genotype tt is q×q, which = q^2. To find the heterozygous frequency Tt, we must consider that (p+1)=1, since these are the only 2 alleles. And if we square those terms, that's how we determine the frequencies. (p+q)^2 = 1^2
--> p^2 + 2pq + q^2 = 1, so the middle term (2pq) is our heterozygous frequency.
