Abstract
We have found the two-dimensional electrophoretic technique of O'Farrell to be highly efficient in the detection of charge-change substitutions in a large number of proteins. We have applied this method to determine the level of heterozygosity of the most abundant proteins in Drosophila 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. We consider these data to throw open the question of the level of genetic variability in nature.