Mathematical Biology seminar Wayne Potts Dept of Biology "Pathogens, mutations, sexual selection and histocompatibility polymorphisms" October 12, 2005 3:05pm, LCB 215 Genes of the major histocompatibility complex (MHC) play a central role in immune recognition, but they also influence individual odors and reproductive traits such as mating preferences and spontaneous abortion. MHC genes are also the most polymorphic loci known for vertebrates. This extreme genetic diversity has the following relatively unique features: (1) large number of alleles per locus, often over 100, (2) extreme sequence diversification between alleles and (3) high rates of non-synonymous substitutions at antigen-binding-site codons. To account for each of the above features at least two forms of natural selection are required. What is the nature of this selection? Current understanding suggests the following relationships. Parasite-driven selection favors MHC genetic diversity through both heterozygote advantage and evasion of MHC-mediated immune recognition. This in turn favors the evolution of MHC-based disassortative mating preferences (etc.) because such matings produce high-quality progeny. Such mating preferences would further increase MHC genetic diversity, making these loci increasingly useful as a kin recognition marker. Consequently, the avoidance of matings with kin (i.e. inbreeding) is an additional factor favoring MHC-based mating preferences. The relative importance of these hypothesized interactions is controversial. I will present results from experimental tests of each hypothesis.