Stable polymorphism for mutant eye colour genes in populations of Drosophila melanogaster in two different media

In previous work analyzing variability of eye colour alleles existing in natural populations of D. melanogaster, it was observed that the number of females heterozygous for some eye colour alleles was greater in a wine cellar population than in populations outside this cellar. In order to determine which mechanisms caused these eye colour alleles to be favored in the heterozygotes, the changes in the frequency of four eye colour alleles frequently seen in the cellar population (se77o, sf77m, cd77o and multichromosomal 77o) was studied in artificial populations. Two different culture media, one supplemented with 10% ethanol and the other without ethanol were used. It was found that each of the four mutants reached similar equilibrium frequencies in both media, though the safranin allele (sf77m) equilibrium frequency was significantly higher in the alcohol medium. A significant excess of heterozygotes were also observed in these populations.