Random distribution of genotypic combinations among microsatellite loci in two Indian natural populations of Drosophila ananassae

Among the genus Drosophila, D. ananassae is a genetically distinctive species, mainly due to the occurrence of spontaneous crossing over in its males, which does not occur in most other species of the genus. This species has been adequately studied for its chromosomal, allozyme, and nucleotide polymorphisms to envisage genetic differentiation in its natural and laboratory populations. Its ample use in population genetic investigations has helped to decipher various micro-evolutionary phenomena. The present study deals with the genotypic associations among seven microsatellite gene loci in natural populations of D. ananassae. Each microsatellite locus, having two allelic forms, varies due to differences in their di-nucleotide repeats and follows a co-dominant inheritance pattern. Thus, the comparison between two such independent loci yield nine genotypic combinations. The results of the study showed a random occurrence of all possible genotypic associations in twenty-one gene loci comparisons. This equilibrium in different gene combinations may be attributed to the neutral role of microsatellite gene loci, providing equal survival chances to individuals carrying them. Besides the absence of selection, the independent assortment of different gene combinations might have promoted the occurrence of linkage equilibrium in D. ananassae. Further, the positions of microsatellite gene loci on different chromosomes in D. ananassae and their status with respect to linkage disequilibrium have been discussed in this paper.