The gene coding for Zn-alpha 2-glycoprotein (AZGP1), a human protein with a high degree of similarity to class I major histocompatibility complex (MHC) antigens, was mapped by fluorescent in situ hybridization to chromosome 7q22, a common breakpoint in myelodysplastic syndromes. Since classical MHC genes map on chromosome 6, this assignment indicates that besides duplication of the putative common ancestor gene, transposition events to different chromosomes have also been involved in the evolutionary diversification of this gene family.