Nine populations of D. melanogaster and two populations of D. simulans were analyzed for polymorphism in 10 gene-enzyme systems by the technique of gel electrophoresis. In the eight natural populations of D. melanogaster, an average of 54% of the enzymes were polymorphic, and the average heterozygosity was 22.7%. An experimental population of D. melanogaster, which has been maintained in a laboratory cage for 20 years, showed levels of polymorphism equivalent to those of natural populations. The D. simulans populations had much less variability. The possible factors involved in maintaining these polymorphisms are discussed.
O'Brien, Stephen J. and Ross J. MacIntyre. 1969. "An Analysis of Gene-Enzyme Variability in Natural Populations of Drosophila melanogaster and D. simulans." American Naturalist 103, (930): 97-113. doi:https://doi.org/10.1086/282587.