Calculating the frequency of a recessive allele in case of three segregating alleles
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A few issues about your post

You should always limit your post to a single question.

Make sure to define what the function f() and p() mean.

Use points (.) instead of comas (,) for the numbers.

You should show how you made your calculations otherwise we can't tell what is right and wrong.

Your question


  is $p = f(AA) + \frac1{1}{2} f(Aa)=\sqrt{f(AA)}$ correct?


$$f(AA) = p^2$$
$$f(Aa) = 2pq = 2p(1-p)$$
$$f(Aa)/2 = pq = p(1-p) = p - p^2$$
, therefore

$$f(AA) + f(Aa)/2 = p^2 + (p - p^2) = p = \sqrt{p^2} = \sqrt{f(AA)}$$

So, yes you are correct