A mapping and evolutionary study of porcine sex chromosome genes

A combination of FISH and RH mapping was used to study the evolution of sex chromosome genes in the pig. In total, 19 genes were identified, including 3 PAR genes (STS, KAL, PRK). The gene order of the porcine X Chromosome (Chr) closely resembled the human X Chr (PRK/STS/KALAMELX-EIF2s3X/ZFX-USP9X-DBX-SMCX) suggesting that the porcine X has undergone very little rearrangement during evolution. For the porcine Y Chr, two linkage groups of 10 NRY genes were found, and the following order was established: Ypter- (AMELY-EIF2S3Y/ZFY-USP9Y-DBY/UTY)-(TSPY-SMCY-UBE1Y-SRY)-CEN. This gene order showed greater conservation with the murine Y than with the human Y Chr. In addition, all porcine Y Chr genes mapped to Yp, which is similar to the mouse and included EIF2s3Y and UBE1Y, which are not present in humans. Interestingly, complete conservation of X/Y homologous gene order was found between the pig X and Y Chrs, indicating that the porcine Y Chr has not undergone extensive reorganisation with respect to the X. This suggests that the order of the X/Y homologous genes of the porcine X and Y Chrs may closely resemble the ancestral gene order of the eutherian sex chromosomes.