10.20 Conclusion
In this lab, we assessed evidence for Neanderthal introgression into specific human populations.
- We reviewed the \(\mathbf{D}\) statistic, which asks whether a variant shows an imbalance in the population inheritance patterns expected from incomplete lineage sorting (ILS). Such an imbalance implies historical introgression into one population.
- With
admixr, we calculated the \(D\) statistic for one individual from each of seven modern human populations, identifying significant evidence for Neanderthal introgression into the ancestors of non-African – but not African – populations. - We also calculated the \(\mathbf{f_4}\) statistic, which is very similar to the \(D\) statistic but is proportional to the genetic distance between two populations.
- We computed the \(\mathbf{f_4}\)-ratio, whose value indicates the proportion of introgressed ancestry in each population.
- Finally, we computed the \(\mathbf{f_4}\)-ratio within just promoter regions, where we observed a depletion of Neanderthal ancestry.