THE Y-ASTERISK REARRANGEMENT IN MICE - NEW INSIGHTS INTO A PERPLEXINGPAR

In essence, the Y rearrangement in the mouse is a Y chromosome that h as been hijacked by a non-Y centromere attached distal to the pseudoau tosomal region (PAR). Al the Y-unique material is thought to be unalte red, but the recombinatory behaviour of the Y with the X during male meioisis led to the conclusion that part of the PAR is inverted. In th e course of a cross set up to introduce the X-linked mutation Patchy f ur (Paf) into XY males, the Y* chromosome was found to carry the wild type allele of Paf. Paf maps close to the X PAR boundary, so we hypot hesised that the inverted region of the Y PAR originated from an X ch romosome that provided not only an inverted copy of proximal PAR, but also an X PAR boundary together with some adjacent X-unique material t hat included the Paflocus. This hypothesis was validated by Southern a nalysis using an X PAR boundary probe to show that Y has an X PAR bou ndary. Thus the Y'' PAR has resulted from an end to end fusion of an X and a Y PAR. Furthermore, it was shown that in conjuction With this P AR-PAR fusion, there has been deletion of both copies of the distally located pseudoautosomal gene Steroid sulfatase (Sts).