Inversion polymorphism in Drosophila ananassae: persistence of inversions, heterosis and intra- and inter-chromosomal associations in experimental populations of mixed geographic origin.

ABSTRACT

Two experimental populations of D. ananassae were synthesised by making reciprocal crosses among five geographic strains and mixing the hybrids. Each of the two populations of mixed geographic origin was maintained as mass cultures in food bottles. After five generations chromosomal analysis of these two populations was made by squashing a large number of larvae. The results showed that both experimental populations remained polymorphic due to the persistence of AL, (2L), ZE (2R) and DE (3L) inversions in population A and AL, ZE, DE and ET (3R) inversions in population B. Persistence of inversions in considerable frequency and significant deviation from Hardy-Weinberg equilibrium showed that heterosis is associated with these four inversions in D. ananassae. Further, there is non-random association (linkage disequilibrium) between linked inversions in second (AL-ZE) chromosome. However, the inversions of the different chromosomes are associated randomly indicating no interchromosomal interactions in D. ananassae. The results of these studies on population dynamics of inversion polymorphism in experimental populations are attributable to selection, genetic drift and Founder effect.