Association of allozyme heterozygosity and sternopleural chaetae number in Drosophila melanogaster.

Variation at two polymorphic allozyme loci (Adh and alpha Gpdh) has been assayed in relation to sternopleural chaetae number in flies derived from a cage population of D. melanogaster known to be under stabilising selection with respect to chaetae number. Central phenotypes were significantly more heterozygous at these loci than more extreme phenotypes. Analysis of the base population and of divergent directional selection lines derived from it suggested that alleles at Adh and alpha Gpdh have a pleiotropic effect on chaetae number or are in strong linkage disequilibrium with chaetae factors. In addition, homozygotes at Adh and alpha Gpdh were observed to have a higher variance in chaetae number than heterozygotes. It is concluded that additive and homeostatic models of gene action might both partly explain the higher heterozygosity of central phenotypes.