Xq21.3 to Yp11.2 Duplication

The Xq21.3/Yp11.2 homologous block is specific to Homo sapiens, that is to say that it is represented on the X and Y chromosomes in Man but on the X alone in other mammalian species. The block on the Y is referred to as the “X-transposed region” (XTR)(Ross, Graftham et al. 2005) and comprises 3.4Mb. It was created by a duplicative transposition now dated at 6MYA and has undergone two deletions and a paracentric inversion. The X sequence includes 3 genes of which only one – Protocadherin11Y remains expressed from the Y chromosome. The Protocadherin11XY gene pair thus codes for X and Y versions of a cell-surface adhesion molecule. Its particular interest lies in relation to the hypothesis that sexual dimorphisms and sexual selection play a role in the differentiation of species.