Esterase heterogeneity: dynamics of a polymorphism.

In the freshwater fish Catostomus clarkii, the frequency of alleles for polymorphic serum esterase varies with latitude. The activity of the allele more frequent in southern populations increases as temperature increases from 0 degrees to 37 degrees C, whereas activity of the allele more frequent in northern populations increases as temperature decreases. Coefficients of selection used to calculate allelic equilibrium within populations are derived from the activity profiles of the genotypes.