A directional process of gene conversion is expected to yield dynamic polymorphism associated with stability of alternative alleles in class I histocompatibility antigens gene family.

This work is a contribution to the discussion of the polymorphism of class I histocompatibility antigens (H-2 antigens in the mouse). Specially, the involvement of gene conversion in H-2 polymorphism has been explored through the use of a simplified computer model. It thus appears that in a population of limited size, gene conversion can promote allelic polymorphism while homogenizing the DNA sequences in a multigene family, only if it acts as a directional process. The DNA sequences of the preferential targets are then polymorphic and evolutionary versatile, while other genes of the family mostly behave as sequence donors, have more stable DNA sequences and are much less polymorphic. The characteristics of such a polymorphism generator are discussed with respect to their functional and evolutionary implications.