Abstracts (first author)
Evolution of MHC gene number: optimality hypothesis and beyond
MHC genes code for proteins involved in recognition of pathogens. Their extreme polymorphism, thought to be driven primarily by selection from parasites, has been subject of much theoretical and empirical work. In addition to allelic diversity, MHC genes are often multiplicated, but the evolution of the MHC copy number received relatively less attention. Optimality hypothesis (Nowak et al. 1992) poses that an increase in parasite recognition capabilities with increased number of MHC molecules expressed is traded off against higher rate of deletion of auto-reactive lymphocytes, thus some intermediate individual MHC diversity should be favoured. Empirical tests of this hypothesis have been hampered by technical difficulties associated with the typing of multi-locus genotypes, but this has now been overcome by new generation sequencing methods. I will review the recent empirical studies of the optimality hypothesis. The presence of multiple MHC genes in the genome may also facilitate creation of new alleles via inter-genic recombination (Ohta 1991). The results of simulations of host-parasite coevolution showed that such newly created alleles are very likely to be retained in populations. This opens the possibility for haplotypes with a high number of MHC copies to hitch-hike with positively selected alleles.