Transspecies evolution

The favored type of evolution of the MHC allelic diversity. The age of an allele or an allelic lineage is greater than the species. Therefore, common allelic lineages have been inherited from a common ancestor and species-specific mutational diversification occurred within these lineages. For example, no single MHC class I allele is shared between humans and chimpanzees, but numerous similarities in lineage, polymorphic motifs and individual substitutions can be observed. One consequence is that certain alleles will be more similar to their correspondent alleles in another species than to the other alleles of the same locus in the same species. The long-term persistence of families of MHC alleles whose origins predate speciation events is called 'trans-species evolution'.