Dictionary of Human Evolution and Biology

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P22pq Q21

Fundamental principle in biology that summation of any two allele frequencies in a one-locus, two-allele genetic system will equal unity {(p q) 1}; further, that when both sides of such an equation are squared, the resulting binomial expansion results in three terms (p2, 2pq, q2) that represent three expected genotype frequencies when the values of the two allele frequencies (p, q) remain constant.

See Hardy-Weinberg equilibrium.