9701098 Charlesworth Sex determination in many species is controlled by a special pair of chromosomes, the X and Y chromosomes. The Y chromosome usually has few active genes. In some species, "neo-sex chromosomes" have been formed by the fusion of an X or Y chromosome to a regular chromosome, causing this chromosome to be transmitted in the same way as the true sex chromosomes. This allows study of the forces responsible for the degeneration of the Y chromosome. The fruitfly Drosophila miranda is a classic example, in which some of the genes on the neo-Y chromosome have degenerated. Different processes that might be responsible for degeneration have different consequences for the patterns of between- and within-species variation of neo-Y chromosome genes. The DNA sequences of neo-Y chromosome genes will be obtained from different individuals of D. miranda, and from its relative D. pseudoobscura, in order to find out which processes are occurring. This work will illuminate the origin of the basic features of sex chromosomes, and enhance knowledge of the genetic mechanisms controlling variation in DNA sequences. Since sex chromosomes play an important role in human genetic diseases, the results will aid our understanding of these diseases.
