High frequency de novo alterations in the long-range genomic structure of the mouse pseudoautosomal region.

The pseudoautosomal region (PAR) is a segment of shared homology between the X and Y chromosomes. Here we report physical linkage of three mouse PAR probes: DXYHgu1, DXYMov15 and (TTAGGG)n. Steroid sulphatase (Sts) maps distal to these probes, indicating that there is an internal array of the telomere sequence (TTAGGG)n in the PAR. Pseudoautosomal PacI restriction fragments, up to 2 Mb in size, are unstable in C57BL/6 x C57BL/6 crosses. New alleles, often several hundred kilobases different in size, occur at a sex-averaged rate of approximately 30% per allele. Such frequent large-scale germline genome arrangements are without precedent in mammals.