The Hardy-Weinberg formula can be used to calculate a gene's frequency based on phenotype information. An allele refers to one of the alternative forms for a gene that may occupy a single locus on homologous chromosomes. An allele's frequency (calculated from phenotype frequencies) is its proportion of the total allelic pool. The sum of allele frequencies at a given locus must equal 1.00.

Hardy-Weinberg formula for a two allele system:


((p^2) + (2pq) + (q^2)) = 1


For alleles X[a] and X[b]:

p = frequency of allele X[a]

q = frequency of allele X[b]

p^2 = frequency of X[a]X[a] = phenotype X(a+b-)

q^2 = frequency of X[b]X[b] = phenotype X(a-b+)

2pq = frequency of X[a]X[b] = phenotype X(a+b+)


If frequency of phenotype X(a+) is 0.x, then:

((p^2) + (2pq)) = 0.x

q^2 = (1.0 - 0.x)


q = ((1.0 - 0.x)^(0.5))


since (p + q) = 1, p = (1 - q)

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