Genetic studies of Jews

Genetic studies have been used to investigate the origins of diverse Jewish ethnic subgroups, and assess shared ancestry between Jews and converts to Judaism who are considered fully Jewish, and non-Jewish populations. The medical genetics of Jews is a subset of this research, that focuses on population-specific diseases and on genetic conditions shared with other ethnic groups. Studies on Jewish populations have been principally conducted using all three types of genealogical DNA tests: autosomal (atDNA), mitochondrial (mtDNA), and Y-chromosome (Y-DNA). Autosomal testing, which looks at the largest sets of genes within peoples' DNA, shows that Jewish populations tend to form genetic isolates – relatively closely related groups in independent communities with most in a community sharing significant ancestry. The Ashkenazi Jews form the largest such group. Mitochondrial and Y-DNA tests look at maternal and paternal ancestry respectively, via two small groups of genes transmitted only via female or male ancestors. Studies on the genetic composition of Ashkenazi, Sephardi, and Mizrahi Jewish populations of the Jewish diaspora show significant amounts of shared Middle Eastern ancestry, as well as admixture from local populations.Jews living in the North African, Italian, and Iberian regions show variable frequencies of genetic overlap with the historical non-Jewish population along the maternal lines. In the case of Ashkenazi and Sephardi Jews (in particular Moroccan Jews), who are closely related, the source of non-Middle-Eastern admixture is mainly Southern European. Some researchers have remarked on an especially close relationship between Ashkenazi Jews and modern Italians, Greeks, and other Southern Europeans. Bene Israel and the Cochin Jews of India, and Beta Israel of Ethiopia, resemble their local populations but also may have some admixture.

Religious, historical, and genetic perspectives on Jewish identity

Jewish identity and Jewish peoplehood are multifaceted, and there are multiple theories on the ethnic origins of Jews. According to one Israeli rabbi, David Hartman, "One of the salient features of modern Jewry is the lack of consensus about what constitutes membership in the Jewish people." Jewishness can be placed at the intersection of ethnicity, nationality, religion and race, extending beyond the specifics of religious observance. The traditional belief is that Jews descended from the ancient Israelites, without implying that all Jews are biological descendants, since conversion has always been part of Judaism. Genetic evidence corroborating this biblical-based account has been disputed. The advent of modern genetic research methods has led to extensive genetic studies on the topic. Such research has identified genotypic common denominators of Jewish people, but while certain detectable Middle Eastern genetic components exist in numerous Jewish communities, there is no single definitive Jewish prototype. Genomic research has found that most Jewish populations share genetic commonalities with each other, and are distinguishable from non-Jewish groups. Several studies have found genetic continuity with studied medieval individuals from before the 14th century, indicating that one or more genetic bottlenecks predates that timeframe. Some of them were thought to have been victims of pogroms or antisemitic violence, were identifiably Jewish, but had important differences from modern populations, with an increase in homogeneity seen today.

Autosomal DNA These studies focus upon autosomal chromosomes, the 22 homologous or autosomes (non-sex chromosomes)

Summary Autosomal DNA studies show high levels of genetic relatedness among Ashkenazi, Sephardi, and Mizrahi Jews, corresponding to a shared Middle Eastern ancestry with variations in regional admixture. Autosomal DNA evidence supports the historical narrative of Jewish populations originating from the ancient Levant, with genetic diversity shaped by migrations, admixture, and isolation over millennia. Note, however, that the modern population of Southern Europe, often used as the European reference population in such studies, itself contains substantial ancient Middle Eastern ancestry, while present-day populations of the Levant exhibit considerable recent Sub-Saharan African ancestry, leading to an underestimation of the Levantine component of the Ashkenazi Jewish genome.

Ashkenazi Jews share genetic similarities with Southern Europeans, such as Italians and Greeks, while exhibiting unique markers distinguishing them from non-Jewish groups. Similarly, North African Jews also exhibit proximity to European and Middle Eastern groups, reflecting their historical migration pattern. Other studies also reveal significant regional genetic diversity, such as the Berber admixture in Libyan Jews, or Ethiopian Jews' local ancestry combined with Middle Eastern links. In autosomal analyses, the Iraqi Jews, Iranian Jews, Bukharian Jews, Kurdish Jews, Mountain Jews, and Georgian Jews form a close genetic cluster. When examined at a more detailed level, the groups can be separated from each other. This cluster plots between Levantine and Northern West Asian populations. Syrian and North African Jews are separate from it and closer to the Sephardi Jews. Yemenite Jews are distinct from other Jewish groups and cluster with the non-Jewish population of the Arabian Peninsula.

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