# The Hardy - both sides Some applications The Hardy Weinberg...

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The Hardy-Weinberg equilibrium The Hardy-Weinberg equilibrium can be stated thus: Hardy Weinberg frequencies Genotype frequency AA p 2 Aa 2pq aa q 2 For a gene with just two alleles A and a , if the frequency of allele A in the population is p and the frequency of allele a is q then first, the sum of the frequencies of the alleles must equal 1 ( p + q = 1 ) because that's all the alleles added up. Secondly, (and this is the important bit) the frequencies of the genotypes AA , Aa and aa will be p 2 , 2pq and q 2 respectively. [And incidentally p 2 +2pq+q 2 will equal 1 because that's all the possible genotypes added together and because it's an inevitable mathematical consequence of the fact that p+q=1 (try squaring
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Unformatted text preview: both sides!).] Some applications The Hardy Weinberg equilibrium can be used to estimate genotype and gene frequencies from limited data. • For example, for a recessive condition: if the frequency of affected people is f then the gene frequency q = f ½ and the frequency of carriers will be 2pq (and because p is close to 1 this will be more or less 2q). For cystic fibrosis, the frequency of affected children is about 1 in 2000, therefore q = [1/2000] ½ = 0.0223, therefore the frequency of carriers is approximately 2q = 0.0446 or one in 22....
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