Biochemical comparison of major histocompatibility complex molecules from different subspecies of Mus musculus: evidence for trans-specific evolution of alleles

H-2 haplotypes were extracted from wild mice of three subspecies, Mus musculus domesticus, M. m. molossinus, and M. m. castaneus, that are known to have been separated from one another for some 1 to 2 million years. Serologically indistinguishable molecules controlled by some of the polymorphic H-2 loci were compared by tryptic peptide mapping, and the maps were found to be identical. In addition, a number of instances of biochemically indistinguishable H-2 molecules were found among wild mice and inbred strains of the M. m. domesticus subspecies. These findings suggest that some of the H-2 alleles have not altered for greater than 1 million years. To reconcile this apparent stability of H-2 genes with their extraordinary polymorphism (some 100 alleles at each of the polymorphic H-2 loci), it is proposed that the H-2 alleles evolve as if they were separate loci.