The genetics of Jews are a large set of related fields. Much of it is motivated by medical considerations, in particular “Jewish diseases” such as Tay-Sachs. Though the ultimate aim of much research is to clarify population stratification in association studies, over the past few years there has been a great deal of light shed on the possible origins of and the relationships of Jews to each other and other populations. Originally the focus was on uniparental lineages, male and female markers passed through the Y chromosome and mtDNA respectively. The general results of these were that both the extreme scenarios of total replacement and pure cultural diffusion are false. On the one hand Jews across the world by and large share unexpected genetic affinity which one would not predict from geography, but only from their common religious-ethnic identity as Jews. But Jews also cluster geographically in a way that is reminiscent of the gentile populations among whom they have settled, suggesting either independent evolution after an initial separation and/or admixture with the local populations.
One of the most popular posts on this weblog focuses on the differences between Ashkenazi Jews and gentiles, in particular peoples of European descent. The figure to the left illustrates that white Americans who are gentile or Jewish are rather easy to distinguish genetically from each other. That Jews exhibit a particularly distinctive genetic signature may not be all that surprising, considering that medical geneticists have long known that there are diseases which are biologically rooted and heavily overrepresented among this population. Distinctive traits imply distinctive genes. And the demographic history of the Jewish people as attested to in the literary records can be fitted rather easily within the framework of many of the results coming out of the genetic studies.
But what about the issues I mooted above in regards to the divisions among the Diasporic Jewish community? A new paper in The American Journal of Human Genetics takes a stab at attempting establish a set of relations between different Jewish communities, as well as other populations which they may have admixed with. Abraham’s Children in the Genome Era: Major Jewish Diaspora Populations Comprise Distinct Genetic Clusters with Shared Middle Eastern Ancestry:
For more than a century, Jews and non-Jews alike have tried to define the relatedness of contemporary Jewish people. Previous genetic studies of blood group and serum markers suggested that Jewish groups had Middle Eastern origin with greater genetic similarity between paired Jewish populations. However, these and successor studies of monoallelic Y chromosomal and mitochondrial genetic markers did not resolve the issues of within and between-group Jewish genetic identity. Here, genome-wide analysis of seven Jewish groups (Iranian, Iraqi, Syrian, Italian, Turkish, Greek, and Ashkenazi) and comparison with non-Jewish groups demonstrated distinctive Jewish population clusters, each with shared Middle Eastern ancestry, proximity to contemporary Middle Eastern populations, and variable degrees of European and North African admixture. Two major groups were identified by principal component, phylogenetic, and identity by descent (IBD) analysis: Middle Eastern Jews and European/Syrian Jews. The IBD segment sharing and the proximity of European Jews to each other and to southern European populations suggested similar origins for European Jewry and refuted large-scale genetic contributions of Central and Eastern European and Slavic populations to the formation of Ashkenazi Jewry. Rapid decay of IBD in Ashkenazi Jewish genomes was consistent with a severe bottleneck followed by large expansion, such as occurred with the so-called demographic miracle of population expansion from 50,000 people at the beginning of the 15th century to 5,000,000 people at the beginning of the 19th century. Thus, this study demonstrates that European/Syrian and Middle Eastern Jews represent a series of geographical isolates or clusters woven together by shared IBD genetic threads.http://blogs.discovermagazine.com/gnxp/2010/06/genetics-the-jewish-question/