Changes in gene frequencies at the octanol dehydrogenase locus of Drosophila melanogaster imposed by environmental ethanol

Experiments have been performed to study the effect of selection at the Odh locus in Drosophila melanogaster populations using different alcohol concentrations in the medium. The data can be best interpreted by assuming frequency-dependent selection. When genotype frequencies are considered as independent variables and values of Wrightian fitness as dependent variables, it turns out that different functions describe the selection of the coexisting genotypes. A linear equation is used for the SF genotype and a hyperbolic function for the FF genotype. No function of good fit could be found for the SS genotype. Simulation experiments using these functions fit our data well.