X-Y PAIRING, MEIOTIC DRIVE, AND RIBOSOMAL DNA IN DROSOPHILA-MELANOGASTER MALES

One of the genotypic features responsible for sex-chromosome meiotic drive and sterility in Drosophila melanogaster males has now been defined clearly. Separation of a significant fraction of X euchromatin from the X pairing site causes either meiotic drive or sterility, depending on whether the separation occurs alone or in combination with rearrangements involving the Y chromosome. The relationship between X-chromosome integrity and the late-spermatid developmental breakdowns responsible for meiotic drive and sterility is still not understood. X-Y pairing is important for some aspect of spermatogenesis in addition to its role in X-Y disjunction. Transcriptional inactivation and meiotic timing are two possibilities that are worth exploring, and there are likely to be others. With molecular probes for genes active in spermatogenesis becoming available, ideas such as the pairing dependence of transcriptional inactivation should become amenable to direct tests. It is hoped that an increased use of molecular methods will shed new light on this fascinating genetic problem.