Genetical variation for enzyme activity in a population of Drosophila melanogaster

Abstract

Fifteen highly inbred lines extracted by sib-mating from the laboratory cage population, "Texas", of Drosophila melanogaster were crossed in a half-diallel mating design. Female progeny were assayed individually for ADH activity at 25° and 35°C and for total protein. At 25°C there was considerable additive genetical variation and the dominance variation was attributable to specific parents and to specific crosses at random in the diallel table. The character total protein also showed considerable additive variation but less dominance variation. Largely independent gene action was shown by the characters ADH activity and total protein. There were strong genotype-environment interactions for heat-stability. At 35°C most of the genetical variation was additive and mainly due to modifier loci. It was concluded that at 25°C dominance was ambidirectional and almost complete. This genetical architecture was compatible with a past history of stabilising selection for ADH activity in the "Texas" population.