A Mus musculus pseudoautosomal marker is X unique in Mus spretus. The pseudoautosomal marker, DXYCbl1, was amplified by polymerase chain reaction (PCR) from genomic DNA derived from B6 (B6), SPE (SPE), (B6 × SPE)F₁ male mice, and an admixture of B6 + SPE DNA. PCR fragments were sequenced directly, and chromatograms are displayed.