Physical map of the class III of sheep MHC. The relative order of 10 BAC clones spanning ≈700 kbp containing sheep orthologues of loci mapped to the class III of the human MHC. The presence of the class I region was confirmed by the presence of a class I locus in BAC clone 487C7. The start of the class II region was inferred from the location of the Notch4 gene in BAC 257B2. Individual loci (31) are shown as vertical bars; the distances between bars are not to scale. Bars shaded red (9) and green (8) depict loci for which the relative positions are known; red bars are derived from sequencing BAC clones while green bars are derived from sequencing of cosmid clones. The open bars comprise two groups of 14 loci for which the relative position is known but for which the intragroup order of loci is not known. The map of these loci has been inferred assuming a similar map to that of the human MHC.