The fate of several migrant genes in isolated populations of Drosophila melanogaster

Abstract

Sepia-eyed flies carrying the slow electrophoretic variant of either Est-6 or Adh were introduced in low numbers and at infrequent intervals into populations of wildtype flies (+^se/+^se) that were also homozygous for the fast moving variant of either Est-6 (50 populations) or Adh (50 populations). After 24 generations, the frequency of the sepia alleles was approximately 25%, although there was considerable variation from population to population. The fate of the Est-6 slow allele corresponded closely to that of sepia (which is located ten map units distant), although one population retained the slow allozyme variant but rejected sepia. The Adh slow allele was also retained by many populations. A number of them retained Adh-S but not sepia, and vice versa; these loci are on different chromosomes. The advantage of sepia heterozygotes was estimated to be about twice that of wildtype homozygotes. The data suggest that the selective advantage resides not with the sepia locus itself, but with a nearby chromosomal region.