Isolation of the mouse pseudoautosomal boundary (PAB). (A) A genomic contig covering the distal part of the mouse X chromosome consisting of overlapping YAC and bacterial artificial chromosomes (BAC) clones covering the region proximal of, and including, the PAB. Boxed regions of YACs indicate the presence of X chromosomal DNA, whereas lines indicate the presence of non–X chromosomal DNA. The STSs derived from these YACs and their relative distances are indicated below the line. The suffix L or R on the STS name indicates the left or right arm of the YAC from which the STS is derived. The position of additional genetic markers localized to the contig are also indicated. TEL and CEN indicate telomeric and centromeric directions, respectively. The figure is not to scale; however, the total walk covers ∼2.5 Mb. (B) Schematic representation of a 10-kb genomic fragment spanning the mouse PAB, showing markers isolated from this region. Black boxes indicate markers derived from Fxyexon sequence.