Linkage disequilibrium in laboratory populations of Drosophila nasuta

Abstract

Natural populations of Drosophila nasuta are polymorphic for many gene arrangements. Two non-overlapping inversions of the third chromosome, III-2 and III-35, are most common and display extreme linkage disequilibrium. Six randomly mating laboratory stocks, each founded by one gravid female heterozygous in coupling for both III-2 and III-35, were observed after 32 generations. Significant linkage disequilibrium was observed in all stocks. Recombinants were found in only two stocks. The absence of effective recombination in some stocks and its presence in others might be due to different genotypic backgrounds. We suggest that natural selection, influencing recombination rates in several ways, and intrachromosomal epistasis between the two inversions were the main factors for the maintenance of linkage disequilibrium in D. nasuta.