Isozyme variability in species of the genus Drosophila. II. A multiple allelic isozyme system in Drosophila busckii: a stable polymorphic system.

Abstract

Two strains of Drosophila busckii have been examined for electrophoretic variation in the enzyme leucine aminopeptidase (LAP). In a Hawaiian strain, segregating at equilibrium for three alleles, severe heterotic distortions of segregation ratios from pair matings were observed. However, the adaptive values of the various genotypes varied, depending on the gene frequencies in the offspring. In spite of complications in estimating adaptive values, especially those associated with linkage disequilibrium, and with gene-frequency-dependent variables, predictions of the equilibrium gene frequencies were surprisingly close, and deviated as expected from observed values when the effects of the gene-frequency-dependent component of the adaptive value were considered. The preliminary investigation of an additional University of Texas strain originating from mass culture of several wild-caught females suggested that there may be widespread occurrence of heterotic effects from Lap alleles. The strain has been maintained since 1947 in a mass culture in the laboratory and, after about 300 generations, was segregating for two Lap alleles. Offspring from a series of matings from this population gave indications of heterotic distortions of segregation ratios, with one homozygote being almost lethal.