Biology, Georgia Institute of Technology
April 14, 2016 1:45, Imperial Ballroom B
High quality whole genome sequencing has led to the discovery of Neanderthal DNA in non-African genomes and evidence of Denisovan ancestry in human genomes from Papua New Guinea. Trace amounts of Neanderthal ancestry are also found in East Africa, and ADMIXTURE plots reveal that this is due to back migration from non-African populations. Furthermore, the genomes of African hunter-gatherers contain divergent haplotypes that are most likely due to interbreeding with other unknown archaic hominin populations. Ancient introgression appears to be relevant to all global populations, and an important question is how difficult it is for introgressed alleles to persist in human genomes. Here, I extend population genetics theory to include hybrid fitness effects. Additive and epistatic models are considered, and hybrids are allowed to have either increased or decreased fitness. I find that hybrid fitness effects persist over multiple generations, and these effects are dampened over time due to repeated backcrossing. This changes the probability of fixation, and introgressed alleles effectively enter populations with either a head start or a handicap, depending on whether hybrids have increased or decreased fitness. Because of this, classic equations from theoretical population genetics can easily be modified to include hybrid fitness effects – a finding that is verified by extensive computer simulations.