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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

    1=p2+2pq+q2

    1=p+q

    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

    epenguin

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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

    Ygggdrasil

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    Science Advisor

    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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