Map of the major histocompatibility complex

The left portion represents the entire MHC region on chromosome 6, with the Class I, II, and III regions designated. The right portion is an enlargement of the Class II region and includes pseudogenes, other genes involved in immune function, and genes of unrelated or unknown function, as well as the "classical" Class II genes. The expressed "classical" Class II dimers are noted on the far right in bold letters (DR, DQ, and DP), and the genes encoding them are connected with dashed lines. Two different DR dimers are expressed, each sharing the same DR alpha chain (DRA), but using different DR beta chains (DRB1 and DRB3).