Selection models with fertility differences

While in the classical selection models fitness is introduced as viability or as fertility of a single genotype a model is investigated where fertility is a property of a mating type. Under this quite natural hypothesis the fundamental law of population genetics does not hold. Nevertheless for a symmetric model a thorough analysis of the equilibrium states is given. In particular it is proved that there are at most five polymorphisms. Examples can be given where all these polymorphisms occur. The stability problem can be discussed at least for the symmetric equilibria.