Xg Antigen System (XG)

XGencodes the XG blood group antigen, and is located at the pseudoautosomal boundary on the short (p) arm of chromosome X. The three 5' exons reside in the pseudoautosomal region and the remaining exons within the X-specific end. A truncated copy of this gene is found on the Y chromosome at the pseudoautosomal boundary. It is transcribed, but not expected to make a Y-chromosome specific gene product. Alternatively spliced transcript variants encoding different isoforms have been found for this gene. PBDX, a gene found to span the pseudoautosomal boundary on the X chromosome, is the XG blood group gene. Using rabbit polyclonal and mouse monoclonal antibodies raised against a peptide derived from the N-terminal domain of the predicted mature PBDX, they identified the Xg(a) antigen.