Comparison of MHC organization in representative mammals (figure and legend adapted from Belov et al. 2006, with permission). Of particular note in the opossum MHC is the arrangement of the Class I and II genes into a single interspersed cluster and the absence of Class I genes from the Framework region. These characteristics are reminiscent of arrangements seen in the MHCs of nonmammalian vertebrates. Lines between MHCs of different species indicate the positions of orthologous genes. The asterisk indicates the presence of a duplicated DMB locus (H2-DMb2) in mouse, but not in rat. Dashed lines and question marks represent missing or uncertain data for the particular gene or portion of the genome. Numbers within boxes indicate the number of predicted genes identified within that segment (pseudogenes not included). Unless otherwise indicated, the small boxes indicate individual genes. Map not drawn to scale. Additional details regarding this diagram and implications for the evolution of the mammalian MHC may be found in Belov et al. (2006).
