An insight into the evolutionary history of human MHC paralogon.

The vertebrate genome contains several closely spaced sets of paralogous genes from distinct gene families on typically two, three or four different chromosomes (paralogons). These four fold paralogy regions have been considered as historical remnants of whole genome duplication events (WGDs/2R hypothesis). To examine the 2R hypothesis, a robust phylogenetic analysis of 40 multigene families with triplicated or quadruplicated distribution on human MHC bearing chromosomes (1/6/9/19) was conducted. Topology comparison approach categorized the members of 40 families into six distinct co-duplicated groups. Genes belonging to a particular co-duplicated group are duplicated concurrently, whereas genes of two different co-duplicated groups do not share their evolutionary history and have not duplicated in harmony. Our results based on this large scale phylogenetic data set contradict the polyploidization model and are indicative of small-scale duplications and rearrangement events that cover the entire span of animal history.