The 85th Annual Meeting of the American Association of Physical Anthropologists (2016)

Balancing selection and adaptive introgression as sources of advantageous genetic diversity in populations


Department of Genetics, Max Planck Institute for Evolutionary Anthropology

April 14, 2016 2:45, Imperial Ballroom B Add to calendar

The maintenance of advantageous genetic diversity in certain genomic loci is key for the survival of populations, as shown by the extreme levels of diversity in the Major Histocompatibility (MHC) loci. This genetic and phenotypic diversity can be maintained by long-term balancing selection, as in the case of the MHC and many additional loci in the genomes of humans and other primates. Advantageous genetic diversity can also be due to introgression from sister species –in humans, from archaic human forms. This is because introgression can efficiently introduce, in human populations, alleles that were viable (and possibly advantageous) in archaic human forms, potentially increasing diversity in loci where it is beneficial. We analyzed the genomes of Neandertal, Denisova and modern humans to investigate this phenomenon and to identify candidate loci. One such case is the cluster of immune genes TLR1, TLR6 and TLR10. In non-Africans this locus contains not one, but three different introgressed haplotypes; two are most similar to the sequenced Neandertal genome, while the third is most similar to the Denisovan genome. We show evidence of positive selection of the introgressed haplotypes, suggesting that the archaic alleles were likely advantageous shortly after introgression. Interestingly, genetic variation in this locus is associated with changes in gene expression and with differential susceptibility to disease. Thus, both long-term balancing selection and adaptive introgression contribute to the presence of phenotypically relevant diversity in humans.

This work was funded by the Max Plack Society.