MATERNAL-FETAL INTERACTIONS AND MHC POLYMORPHISM

Two models of maternal-fetal interactions are discussed. In the first, offspring are advantaged if they possess an allele absent in their mo ther. Polymorphism is maintained because rare alleles have an advantag e when present in males. In the second, offspring are disadvantaged if they lack an allele present in their mother. Polymorphism is maintain ed because rare alleles have an advantage when present in females. Bot h classes of model are associated with a deficiency of homozygous geno types. If the artificial assumption of symmetrical selection is relaxe d, the second class of model (gestational drive) could account for the otherwise inexplicable absence of MHC polymorphism in some species. ( C) 1997 Elsevier Science Ireland Ltd.