A site specific increase in recombination in Drosophila ananassae

Male recombination in Brazilian populations of Drosophila ananassae

With few exceptions, spontaneous crossing over does not normally occur in male Drosophila. Drosophila ananassae males show considerable amounts of crossing over. In wild males of D. ananassae from Asian (2008) and Brazilian populations (1986 and 2007) variable frequencies of meiotic crossing over, estimated from chiasmata counts, suggested the existence of factors controlling male crossing over in these populations. To corroborate for such prediction, we present data on spontaneous recombination in F1 males of D. ananassae heterozygous for chromosomes of the same Brazilian populations (1986) and marker chromosomes using three testers stocks. Mean recombination value was low, although high variability existed between individual frequencies. Recombination frequencies between lines in each tester stock were not significantly different, excepting when the 3ple-px and 3ple-cy testers were compared (p < 0.05). These two testers differ in respect to the regional distribution of crossovers. The occurrence of recombination in chromosomes 2 and 3 in F1 males tested with e(65) se; bri ru was not related, suggesting they are under independent genetic control. Our data are consistent with proposed genetic factors controlling male crossing over in the tester stocks and to the presence of enhancers and suppressors of male crossing over segregating in the Brazilian populations (1986).

Chiasmata and chromosome breakages are related to crossing over in Drosophila ananassae males

A cytogenetic analysis of male crossing over in Drosophila ananassae revealed that cytological exchanges resulted in genetic crossing over, and that chiasma frequency and the genetic recombination correlated positively in chromosomes 2 and 3. Furthermore, the frequency of chromosome breakages correlated positively with chiasma frequency. Paracentric inversion heterozygosity had no detectable influence on the chromosome pairing or exchange events within the inversion loop at meiosis. Scoring of the chiasma demonstrated that males homozygous for the previously mapped enhancers of male crossing over had low frequencies of chiasmata, whereas higher frequencies of chiasmata were observed in males heterozygous for enhancers. The results presented here indicate that the genetic factors controlling male crossing over are involved in the origin of chromosome breakages and in exchange events.