Drosophila ananassae: A species characterized by several unusual genetic features

Drosophila ananassae Doleschall is a cosmopolitan and domestic species. It occupies a unique status among the Drosophila species due to certain peculiarities in its genetic behaviour and is of common occurrence in India. The most unusual feature of this species is spontaneous male meiotic recombination in appreciable frequency. The other unusual features are varied chromosomal polymorphism, high mutability, Y-4 linkage of nucleolus organizer, segregation, distortion, parthenogenesis, absence of genetic coadaptation in different geographical populations and extrachromosomal inheritance. The optic morphology (Om) hypermutability system is unique in D. ananassae and there is an involvement of tom retrotransposon for the generation of Om mutations. There is a positive correlation between sternopleural bristle number, mating propensity and fertility in D. ananassae. The existence of sexual isolation has been reported within D. ananassae and the degree of sexual isolation is stronger in isofemale lines than in natural populations. Behavioural studies also have revealed several interesting features in D. ananassae. A spontaneous bilateral genetic mosaic for autosomal genes resulting from mitotic recombination has been reported in D. ananassae. Another unusual feature attributed to D. ananassae is its pattern of chromosomal polymorphism. There are remarkably high levels of chromosomal polymorphism in natural populations. Although 70 paracentric inversions have been detected so far in this species, only three paracentric inversions (AL, DE, and ET) have become coextensive with the species. Most of the inversions have localized distribution and have been detected from a few individuals. Indian populations have undergone a considerable degree of genetic divergence at the level of inversion polymorphism. A large number of pericentric inversions and translocations which ordinarily do not exist in other species of Drosophila are present here.