A schematic representation of the building blocks that form the rhesus macaque DRB region configurations. All rhesus macaque DR haplotypes contain a DRA gene, followed by the presence of a DRB9 segment in close proximity, which consists of exon 2 and its flanking introns. This DR framework is separated from the remaining DRB haplotype by a noncoding stretch that varies in length owing to the presence of different repetitive elements. The DRB region starts either with a functional gene in tandem with a truncated pseudogene or with a single functional gene. Region configuration 8 deviates from this organization, as the first functional gene is absent, and instead, only a defective gene is identified at this locus. A second exception to the most common organizations is represented by an additional isolated pseudogene at region configuration 16. The remaining part of the DRB haplotypes displays more variation, with the presence of one to three cassettes that can contain different paralogous genes (indicated with colored shadings). Three region configurations (1A, 2, 17) lack a cassette and only have a single functional gene present at this position.
