A Homologous Gene-enzyme System, Esterase 6, in Drosophila Melanogaster and D. Simulans.

HE existence in natural populations of a protein polymorphism involving Ttwo forms of a nonspecific esterase has been established in Drosophila mlamgaster (WRIGHT 1961, 1963). The two forms of the esterase, Esterase 6, are distinguishable by their different electrophoretic mobilities in starch gel, Esterase 6" migrating more rapidly toward the anode than Esterase 6s. The inheritance of these two forms is controlled by a pair of codominant alleles, Esterase 6F (Est bF, 6", F ) and Esterase 6s( Est 6', dS, S ) , located at 36.8t on the third chromosome. Individuals homozygous for the Est 6" allele produce a strong, single, Esterase-6 band which migrates faster than a similar, strong, single, Esterase-6 band produced by individuals homozygous for the other allele, Est 6'. Zymograms of heterozygotes, Est &"/Est 6', exhibit both the Esterase-GF band and the Esterase-GS band. Both alleles have been found together in numerous laboratory stocks and in at least two different wild populations. This paper is a report of a search for a similar gene-enzyme system in Drosophila simulans that was undertaken in an effort to extend existing evidence of gene homologies between D. melanogaster and D. simulans to include a case which would provide some information about the nature of the protein products of the homologous genes. In addition, the search was initiated in an attempt to establish the existence of homologous, polymorphic gene-enzyme systems in wild populations of these two closely related species. The discovery of such homologous polymorphic systems would raise interesting questions concerning the stability of such polymorphisms over long periods of evolutionary history and perhaps provide a valuable tool for the investigation of the selective forces involved in their maintenance.