Orientation of loci in the major histocompatibility complex of the rat and its comparison to man and the mouse.

Among 290 F2 progeny of an r10 X ACP cross were two recombinants which allowed the loci for glyoxalase-1 and neuraminidase-1 to be mapped relative to the RT1.A and dw-3 loci in the major histocompatibility complex (MHC) of the rat. In 673 progeny of the same cross there was a recombinant between ft and dw-3, and in 403 progeny of the backcross BY1 X (BY1 X BDIX)F1 there was another recombinant between ft and dw-3. These data, combined with those from previous studies, provide the information for constructing a detailed map of the rat major histocompatibility complex: the gene order and size in the rat are very similar to those in the mouse and different from those in man and in the other species that have been studied. Comparison of the structures of the MHC in the various species leads to a hypothesis about the evolution of the MHC which involves sequential duplications of the genes coding for class I and class II loci and an inversion in the prototypic muridae which placed the class II loci between the class I loci.