The sex-determining region of the Megaselia scalaris (Diptera) Y chromosome

In Megaselia scalaris (Loew) the presence or absence of a male-determining factor, M, is responsible for sex determination. In two wild-type strains, M is located on the homomorphic chromosome pair 2. In the laboratory line Except42 a new Y chromosome was created by recombination between the original Y and the original X chromosome. The Except42 Y chromosome has conserved the sex-determining function and four molecular markers of the original Y chromosome, while 13 original Y markers have been lost. The new Y chromosome, therefore, consists of roughly one-quarter of the original Y chromosome and three-quarters of the original X chromosome. To define the sex-determining region, cosmid clones, one from the original X and one from the original Y chromosome region of the Except42 Y chromosome, were isolated and used as probes for chromosomal in situ suppression (CISS) hybridization. The CISS hybridization signals map the conserved Y segment, including the male-determining factor, to the distal segment of the short arm of the Y chromosome.