Chairman’s Summing up Evolutionary Analysis of HLA Class II Polymorphisms

Abstract

As I said earlier this morning, rather than use this time for summary of the very interesting talks we have heard, I thought I would very briefly go through some of the evolutionary analysis and just discuss how that might elucidate some aspects of the functional properties of the polymorphism. The very high degree of polymorphism that is observed in the human population could be due either to recent and rapid mutation of gene conversion selection or the ancestral species that gave rise to the humanoid linaeges might have contained the alleleic diversity that we see and that ancient alleles have simply been maintained. The most straightforward way to look at that is really to construct a phylogenetic tree of all sequences that are available for given class II loci from humans and the non-human species. If speciation predated diversification, that is, if the diversification happened after speciation, obviously the alleles would show limited similarity between species. However, if the divergence preceded speciation then the clustering of sequences would not go by species but simply by allelic similarity. We have done this for DQ alpha.