Selection of unrelated donors for allogeneic HCT involves sequencing specific exons in 4 different genes on chromosome 6p. The relative position of the HLA-A, HLA-B, HLA-C, and HLA-DRB1 genes in the MHC on the short arm of chromosome 6 at band 6p21.3 is indicated, as are the specific exons within each gene that are routinely sequenced in the process of unrelated donor selection for allogeneic HCT. Most transplantation centers do not as yet perform routine sequencing of exon 2 in the HLA-DQB1 gene, but donor/recipient matching for sequences in this exon is typically performed with medium resolution molecular techniques. The relative position of the HLA-DPB1 gene (in red), which plays a role in histocompatibility in the allogeneic HCT setting but at this time is not routinely sequenced during the donor selection process, is also indicated.