The correct way to calculate allelic frequencies?

[TheExibo]

Homework Statement

Out of a total of 43 people, 15 contain the genotype TT, 16 with Tt, and 12 with tt. Need to determine the allelic frequency of the recessive allele t.

Homework Equations

1=p²+2pq+q²

1=p+q

The Attempt at a Solution

By counting up the individual alleles and divided by the total alleles in this question, I get a different answer than by using the Hardy-Weinberg equation. Total t alleles add up to (16 in the heterozygotes and 24 total in the homozygous recessive genotypes) 40. Dividing 40 by 86 gives a value of around 0.47. Using the Hardy-Weinberg equation, where the 12 is divided by 43 to get the genotype frequency, and then square-rooted, a value of 0.53 is obtained for the frequency: a significantly different number than the 0.47 previously counted up. What is the correct solution?

 

[epenguin]

You have counted up the gene frequencies, there is no doubt about it. There is nothing to stop there being this collection of individuals.

You get a different figure when you take the TT to be p². You will get an absurd figure when you calculate q from the tt.

This is trying to tell you something.

What is Hardy-Weinberg about?

 

[Ygggdrasil]

A Hardy-Weinberg equilibrium makes certain assumptions about the population under study (e.g. random mating between individuals, no selection), so not all populations are in Hardy-Weinberg equilibrium.