Comparative mapping of cosmids and gene clones from a 1.6 Mb chromosomal region of Drosophila melanogaster in three species of the distantly related subgenus Drosophila

The successful hybridization or cosmid clones from Drosophila melanogaster (Sophophora subgenus) to the salivary gland chromosomes of other species as distantly related as those in the Drosophila subgenus attests their great potential for unravelling genome evolution. We have carried out, using 28 c osmids and 13 gene clones, a study of the organization of the D. melanogast er 95A-96A chromosomal region in three Drosophila subgenus species: D. repl eta, D. buzzattii and D. virilis. These clones were first used to built an accurate map of this 1.6 Mb region of D. melanogaster chromosome 3R (Muller 's element E). Then, they were hybridized and mapped to the homologous chro mosome 2 of the other three distantly related species. The studied region i s disseminated over 13 different sites of chromosome 2 in the Drosophila su bgenus species, which implies a minimum of 12 inversion breakpoints fixed b etween the two subgenera. Extrapolation to the entire chromosome gives 90 f ixed inversions. The D. melanogaster Pp1-96A-Acr96Aa segment conserved in D . repleta and D. buzzatii is longer than previously thought and is also con served in D. virilis. In addition, three other D. melanogaster segments con served in the three Drosophila subgenus species were found. Finally, our da ta indicate significant statistical differences in the evolution rate of Mu ller's element E among lineages, a result that agrees well with the previou s cytogenetic data.