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Mol Biol Evol. 2011 Aug;28(8):2239-52. doi: 10.1093/molbev/msr048. Epub 2011 Feb 15.

Testing for ancient admixture between closely related populations.

Author information

  • 1Department of Integrative Biology, University of California, Berkeley, CA, USA. eric.durand@berkeley.edu

Abstract

One enduring question in evolutionary biology is the extent of archaic admixture in the genomes of present-day populations. In this paper, we present a test for ancient admixture that exploits the asymmetry in the frequencies of the two nonconcordant gene trees in a three-population tree. This test was first applied to detect interbreeding between Neandertals and modern humans. We derive the analytic expectation of a test statistic, called the D statistic, which is sensitive to asymmetry under alternative demographic scenarios. We show that the D statistic is insensitive to some demographic assumptions such as ancestral population sizes and requires only the assumption that the ancestral populations were randomly mating. An important aspect of D statistics is that they can be used to detect archaic admixture even when no archaic sample is available. We explore the effect of sequencing error on the false-positive rate of the test for admixture, and we show how to estimate the proportion of archaic ancestry in the genomes of present-day populations. We also investigate a model of subdivision in ancestral populations that can result in D statistics that indicate recent admixture.

PMID:
21325092
[PubMed - indexed for MEDLINE]
PMCID:
PMC3144383
Free PMC Article

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