How selection shapes variation of the human major histocompatibility complex: a review

The nature of polymorphism and molecular sequence variation in the genes of the human major histocompatibility complex (MHC) provides strong support f or the idea that these genes are under selection. With the understanding th at selection shapes MHC variation new questions have become the focus of st udy. What is the mode of selection that accounts for MHC polymorphism? is v ariation maintained by pathogen pressure or by reproductive mechanisms? Dis cerning between these requires drawing on information from studies on assoc iation between HLA genes and infectious diseases, reproductive success and mating preferences relative to HLA genotypes, and theoretical studies that compare the outcomes of different selection regimes. The pattern that has e merged suggests that several types of selection are plausible for the maint enance of HLA polymorphism.