Figure 1.

The chicken MHC (BF-BL region) is smaller and simpler than the human MHC (HLA locus), with a single dominantly-expressed MHC-I molecule due to co-evolution with peptide-loading genes. Colored vertical lines or boxes indicate genes, with names above; thin vertical lines indicate region boundaries, with names above or below; location is roughly to scale, with the length of approximately 100 kB indicated. Thickness of arrows pointing up indicate level of expression, co-evolution between the TAP genes and the BF2 class I gene indicated by a curved arrow beneath the genes. Genes from the class I system, red; the class II system, blue; the class III or other regions, green; solid colors indicate classical genes while striped colors indicate genes involved in peptide loading. Figure from (9).