EVOLUTION OF MHC GENETIC DIVERSITY - A TALE OF INCEST, PESTILENCE ANDSEXUAL PREFERENCE

Evidence from the house mouse (Mus) suggests that the extreme diversit y of genes of the major histocompatibility complex (MHC) results from three different forms of selection involving infectious disease (pesti lence), inbreeding (incest) and MHC-based mating (sexual) preferences. MHC-based disassortative mating preferences are presumed to have evol ved because they reduce homozygosity throughout the genome, and partic ularly within loci linked to the MHC. Progeny derived from such disass ortative matings would enjoy increased fitness because of both reduced levels of inbreeding depression and increased resistance to infectiou s disease arising from their increased MHC heterozygosity.