By the use of deterministic models based on observed imprinted mating preferences in the domestic pigeon Columba livia, as well as in the sexually monomorphic and dimorphic duck species, it is demonstrated that in large populations absolute im-printing tends to split the population into 2 non-interbreeding groups each characterized by a different allele. When relative mating pre-ferences are obtained, a stable equilibrium tends to become established. The terms pegmatype, geno-pegmatype and their derivatives are introduced to describe such mating preferences and mating systems.