Further observations on intragenic recombination inDrosophila melanogaster

Abstract

SUMMARY: This report examines several issues bearing upon intragenic recombination in higher eukaryotes. The fine structure data accumulated in our analysis of the genetic organization of the rosy locus inDrosophila melanogaster. Firstly, we confirm that a conversion event has a markedly less than 50% probability of resulting in flanking marker exchange, a finding consistent with more recent analyses of the availableSaccharomycesdata (e.g. Fogelet al.1978). As reported earlier, co-conversion of recombinationally separable sites within therosylocus occurs (McCarron, Gelbart & Chovnick, 1974). In this report, we demonstrate that the frequency of co-conversion is inversely proportional to the distance between co-converting sites. As in fungi, real conversion frequency differences are observed amongrosymutant alleles, and the data suggest that there may be a relationship between allele conversion frequency and map position. UnlikeNeurosporaandSaccharomyces, only one flanking marker exchange class is recovered from any given mutant heteroallele recombination experiment. In this respect, theDrosophilasystem resemblesAspergillus. As inNeurosporaandSaccharomyces, rosylocus intragenic recombinants associated with flanking marker exchange exhibit interference with crossing over in adjacent regions, while no interference is seen among recombinants exhibiting parental flanking markers. Finally, experimental results are discussed which demonstrate the occurrence of postmeiotic segregation inDrosophila. These analogies betweenDrosophilaand fungi provide further evidence in support of the notion that eukaryotes share common molecular mechanism(s) of meiotic recombination.