Mixed signals?  The role of MHC genes in disease resistance, kin recognition and mate attraction Leslie Knapp1 1Primate Immunogenetics and Molecular Ecology (PrIME) Research Group, Department of Biological Anthropology, University of Cambridge, United Kingdom Abstract The major histocompatibility complex (MHC) plays a critical role in immune response and disease resistance. In all primates studied thus far, the MHC consists of multiple loci characterised by high levels of polymorphism. The extraordinary genetic variation of MHC genes is, at least in part, the result of positive selection and the role of MHC molecules in presenting foreign peptides to T cells. Recent studies, however, also support the argument that MHC genes influence individual odours used in kin recognition and mate choice. Since the MHC is used for cellular discrimination of "self" and "non-self", this genetic system might also be useful for detecting related individuals that share unique combinations of MHC alleles. Although evidence for MHC-based kin recognition or mate attraction in any species is limited, it is possible that odor, color or some other phenotypic marker communicates subtle clues about an individual's MHC genotype. Using data from studies conducted in my research group, I will illustrate how our molecular studies of histocompatibility genes are used to explore the role of MHC diversity in disease resistance and to understand how MHC genes affect signals, such as coloration and odor, used for kin recognition and mate choice.