Dendrogram showing the relationship between the SLY protein and other identified or predicted mammalian Cor1 domain proteins. The autosomally encoded SYCP3 is the presumed ancestral gene because it has been identified in a wide range of vertebrate species. The remaining proteins other than SLY are X encoded. For the rat, the putative X-encoded proteins have not yet been named and the labels given are simply a reflection of their position within the dendrogram. The massive expansion in copy number is only seen in the branch containing XMR, XMR-rel., XLR and SLY. This amplification therefore occurred subsequent to the divergence of mouse and rat lineages, concurrent with the appearance of Sly on the Y chromosome.