Identification of X chromosomal restriction fragment length polymorphism markers and their use in a gene localization study in Drosophila virilis andD. littoralis

We have identified six restriction fragment length polymorphism (RFLP) mark ers based on unique gene sequences on the X chromosome of Drosophila virili s and D. littoralis. The markers were localized by in situ hybridization on larval polytene chromosomes, and the conjugation of the X chromosomes of t he two species was studied in salivary glands of interspecific hybrid femal e larvae. The gene arrangement of D. virilis and D. littoralis appeared to be very different at the proximal end of the X chromosome preventing recomb ination between RFLP markers located in this area. Simple quantitative trai t loci (QTL) analysis showed that five of our marker genes (including nonA and Dmca1A, previously found to affect male courtship song in D. melanogast er) are linked with a gene(s) having a major effect on species differences in the male courtship song between D. virilis and D. littoralis. This shows that the song gene(s) may be located inside a large X-chromosomal inversio n in D. littoralis (as previously suggested), but that it may also be locat ed on an area between this inversion and the centromere, close to nonA and Dmca1A. Localization of this gene or gene complex will be continued with th e aid of our newly identified RFLP markers by making interspecific crosses between D. virilis group species with more similar X chromosomes.