Abstract
The Ashkenazi Jewish (AJ) population is important in medical genetics due to its high rate of Mendelian disorders and other unique genetic characteristics. Ashkenazi Jews have appeared in Europe in the 10th century, and their ancestry is thought to involve an admixture of European (EU) and Middle-Eastern (ME) groups. However, both the time and place of admixture in Europe are obscure and subject to intense debate. Here, we attempt to characterize the Ashkenazi admixture history using a large Ashkenazi sample and careful application of new and existing methods. Our main approach is based on local ancestry inference, assigning each Ashkenazi genomic segment as EU or ME, and comparing allele frequencies across EU segments to those of different EU populations. The contribution of each EU source was also evaluated using GLOBETROTTER and analysis of IBD sharing. The time of admixture was inferred using multiple tools, relying on statistics such as the distributions of segment lengths and the total EU ancestry per chromosome and the correlation of ancestries along the chromosome. Our simulations demonstrated that distinguishing EU vs ME ancestry is subject to considerable noise at the single segment level, but nevertheless, conclusions could be drawn based on chromosome-wide statistics. The predominant source of EU ancestry in AJ was found to be Southern European (≈60-80%), with the rest being likely Eastern European. The inferred admixture time was ≈35 generations ago, but multiple lines of evidence suggests that it represents an average over two or more admixture events, pre- and post-dating the founder event experienced by AJ in late medieval times. The time of the pre-bottleneck admixture event was bounded to 25-55 generations ago.
- Posted July 10, 2016.
