The gene conversion hypothesis of MHC evolution: a review

Gene conversion is often invoked to explain the evolution of sequence patte rns observed in major histocompatibility complex (MHC) genes and their alle les. This is the gene conversion hypothesis of MHC sequence evolution. Thes e observations and their interpretation probably belong in a larger theoret ical framework, namely the evolution of systems of resistance to rapidly ev olving pathogens. This review looks critically at the evidence in favor of the gene conversion hypothesis in this context. We conclude that the case f or the existence of an adaptive mechanism in the MHC favoring gene conversi on mutations is not proven.