Abstract
The 2-dimensional electrophoretic technique of O''Farrell was highly efficient in the detection of charge-change substitutions in a large number of proteins. This method was applied to determine the level of heterozygosity of the most abundant proteins in D. melanogaster adults from a natural population. The estimate of per-locus heterozygosity obtained from approximately 54 loci screened was 4% with 6 loci polymorphic. This is much lower than overall estimates obtained by standard gel electrophoresis but is not different from estimates for Group I enzymes, i.e., those utilizing a narrow spectrum of substrates of intracellular origin. These data throw open the question of the level of genetic variability in nature.