Genetics Problem?

Question

Please look at this problem: http://science.nhmccd.edu/biol/hwe/hwefrm3.html

I understand everything except how the first answer was obtained in the solution ( (f)A ). How does that work? Thank you!

I am talking about this:
(2 * (1469) + (138))/(2 * (1469 + 138 + 5)) = .954

Answer 1

Here they are talking about allele frequency rather than genotype frequency. We want to know: how common is the A allele in the population of alleles?

Each AA individual carries two A alleles, so multiply the number of AA individuals by 2. Each Aa individual carries one copy of A, so multiply that number by 1. The sum is the number of A's in the population.

The denominator is the number of (any) alleles in total, which is just double the entire population (each person carries two).

Answer 2

I can help. What you're asked to find here is the number of "A" alleles in the sample of 1612 individuals.

1) If there are 1612 individuals, there would be twice as many alleles (this is assumed to be a diploid organism), so 3224 total alleles.

2) How many alleles are "A"? First, 1469 animals are dominant homozygous (AA) so each has 2 "A"s, so that's 2938. Second, 138 are heterozygous (Aa), so each have one "A", for 138 more. 2938 + 138 = 3076 "A" alleles total.

3) To find the frequency (percentage) divide the number of "A" alleles by the total number of alleles: 3076/3224

3076/3224=0.9540942, which your answer rounded off to .95

Looking at the formula, it looks confusing, but if you do the step-by step shown here it will make these types of problems simpler to solve.