D.4: Hardy-Weinberg Equilibrium

01/10/2013 § Leave a comment

Wha – wait, what, we’re going to do math in biology as if science wasn’t enough, you expect me to be able to add math into the mix, are you crazy, syllabus?!

Oh, it’s only quadratics.

The Hardy-Weinberg principle involves (relatively simple) math in order to calculate certain frequencies, including phenotype frequencies, allele frequencies, and genotype frequencies. Alleles are normally represented by variables p and q. The total frequency of alleles in a population is 1.0, therefore p + q = 1. The information anyone will need to do these calculations are the allele frequencies and genotype frequencies.

The Hardy-Weinberg equation can only be done if the population fits into a few assumptions:

  • random mating happens in the population
  • natural selection doesn’t cause higher mortality of individuals with one allele than another
  • no mutation
  • population isn’t too small
  • no immigration or emigration


Page 131 (SG), Exam questions on option D – Evolution


a) Calculate the frequency of the sickle cell allele in these ethnic groups. —> 0.2302

b) Calculate the percentage of the population that are carriers of the sickle cell allele. —> 35.44%

c) Outline the reasons for the high frequency of the sickle cell allele in these ethnic groups, despite the serious consequences of sickle cell anaemia. —> The sickle cell allele has a high frequency in these ethnic groups in Africa because of the high frequency of the alleles that code for malaria. Individuals with the sickle cell allele can fend off malaria. The two alleles are an example of balanced polymorphism.

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