INCOMPATIBILITIES BETWEEN Y-CHROMOSOME AND AUTOSOMES ARE RESPONSIBLE FOR MALE HYBRID STERILITY IN CROSSES BETWEEN DROSOPHILA-VIRILIS AND DROSOPHILA-TEXANA

Crosses between Drosophila virilis and D. texana produce viable and fe rtile F-1 males and females. When F-1 males are backcrossed to either parental species they also produce fertile sons. However, about one-th ird of F-1 males carrying the D. texana Y chromosome are sterile. When fertile F-1 males with the D. texana Y chromosome are crossed to D. v irilis, about three quarters of the sons are sterile. We show that the se sterilities result from incompatibilities between the D. texana Y c hromosome and at least two of the D. virilis autosomes. X/Y incompatib ilities can be excluded in this pair of species, and X/autosome incomp atibilities appear to be either absent or to play a minor role in the sterility of male progeny from backcrosses of F-1 males to females fro m either species. It is suggested that Y/autosome incompatibilities ma y be among the first to appear in the development of postzygotic isola tion in Drosophila.