Recombination can initiate and terminate at a large number of sites within the rosy locus of Drosophila melanogaster.

This report presents the results of a recombination experiment designed to question the existence of special sites for the initiation or termination of a recombination heteroduplex within the region of the rosy locus. Intragenic recombination events were monitored between two physically separated rosy mutant alleles ry301 and ry2 utilizing DNA restriction site polymorphisms as genetic markers. Both ry301 and ry2 are known from previous studies to be associated with gene conversion frequencies an order of magnitude lower than single site mutations. The mutations are associated with large, well defined insertions located as internal sites within the locus in prior intragenic mapping studies. On the molecular map, they represent large insertions approximately 2.7 kb apart in the second and third exons, respectively, of the XDH coding region. The present study monitors intragenic recombination in a mutant heterozygous genotype in which DNA homology is disrupted by these large discontinuities, greater than the region of DNA homology and flanking both sides of the locus. If initiation/or termination requires separate sites at either end of the locus, then intragenic recombination within the rosy locus of the heterozygote should be eliminated. Contrary to expectation, significant recombination between these sites is seen.