MALE-STERILITY AND MEIOTIC DRIVE ASSOCIATED WITH SEX-CHROMOSOME REARRANGEMENTS IN DROSOPHILA - ROLE OF X-Y PAIRING

In Drosophila melanogaster, deletions of the pericentromeric X heteroc hromatin cause X-Y nondisjunction, reduced male fertility and distorte d sperm recovery ratios (meiotic drive) in combination with a normal Y chromosome and interact with Y-autosome translocations (T(Y;A)) to ca use complete male sterility. The pericentromeric heterochromatin has b een shown to contain the male-specific X-Y meiotic pairing sites, whic h consist mostly of a 240-bp repeated sequence in the intergenic space rs (IGS) of the rDNA repeats. The experiments in this paper address th e relationship between X-Y pairing failure and the meiotic drive and s terility effects of Xh deletions. X-linked insertions either of comple te rDNA repeats or of rDNA fragments that contain the IGS were found t o suppress X-Y nondisjunction and meiotic drive in Xh(-)/Y males, and to restore fertility to Xh(-)/T(Y;A) males for eight of nine tested Y- autosome translocations. rDNA fragments devoid of IGS repeats proved i ncapable of suppressing either meiotic drive or chromosomal sterility. These results indicate that the various spermatogenic disruptions ass ociated with X heterochromatic deletions are all consequences of X-Y p airing failure. We interpret these findings in terms of a novel model in which misalignment of chromosomes triggers a checkpoint that acts b y disabling the spermatids that derive from affected spermatocytes.