I'm reading Design, Analysis and Interpretation of GWAS of Daniel O. Strom.
On chapter 2 I found:
If we have a sample of N unrelated individuals in a population the distribution of A allele counts for each individual follows a binomial with number of trials = 2N and frequency of A allele = p
p can be found as:
p = ( 1/2N ) * SUM (niA)
Where niA= number of A alleles in individual i
And the variance:
( 1/(2N)^2 ) * SUM Var (niA)
But, I do not understand why do we have the 2N squared in the second equation.