Genic variation in a natural population of Drosophila persimilis.

The understanding of the speciation process can best be achieved by a knowledge of the genic differences between two closely related species and the correlation of such differences with the characteristics which demarcate the two species. D. persimilis and D. pseudoobscura are two sibling species differing from each other in morphology, ecological preferences, and behavior, and no hybrids exist in nature. I have compared the genetic changes in 24 loci of 25 strains of D. persimilis from Mather, California, with those in D. pseudoobscura by the method of acrylamide gel electrophoresis. The proportion of the genome heterozygous in individual D. persimilis is 10.5 per cent, which is comparable to the heterogeneity found in similar D. pseudoobscura populations. I did not find any locus which is monomorphic or polymorphic for entirely different allele(s) than in D. pseudoobscura. The different frequencies of shared alleles in the two species can only be explained by selection acting differentially in these species, since the frequencies of different alleles at various loci in several populations of D. pseudoobscura are very similar or show a very stable pattern of association with the third chromosome gene arrangements.