The first X-linked gene in humans shown to escape X-chromosome inactivation. XG resides on Xp between MIC2 (q.v.) and the centromere. It spans the pseudoautosomal boundary and has its first three exons in the pseudoautosomal region and the rest in the X-specific region. The Xg blood group antigen is encoded by XG. The gene product is a protein that shows a 50% sequence identity to CD99, the product of the MIC2 gene. It therefore appears that the two genes share a common ancestor.
Subjects: Genetics and Genomics.