Hardy Weinberg 1/2 pq

[Mag0009]

Hello,

I'm new and I have this problem that I cannot figure out by myself so I thought someone could help me here.

When we know how many recessive homozygotes we have, then we change it into decimals and a square root would be the frequency of q (the recessive allele). It is simple and logical.

Why do I sometimes see that people calculate q as the suare root plus 1/2 pq? I saw it in Campbell and the example was about codominance. So are the calculations different when you have codominance and three phenotypes for three genotypes?

 

Thanks.

: )