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Homework Help: The correct way to calculate allelic frequencies?

  1. Sep 29, 2015 #1
    1. The problem statement, all variables and given/known data

    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.

    2. Relevant equations



    3. 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?
  2. jcsd
  3. Sep 30, 2015 #2


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    Homework Helper
    Gold Member

    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?
  4. Oct 1, 2015 #3


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    Science Advisor
    2017 Award

    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.
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