(a^2), (1-a)^2 and 2a(1-a) are the relative frequency for the outcomes genotype S1, S2 and S3 respectively where "a" is the gene frequency.
suppose that in a random sample of size n, there are x1, x2, and x3 number of genotypes s1,s2 and s3 respectively where x1+x2+x3=n
What sort of distribution is this?
What is the probability function?