The original founding group of Ashkenazi Jews is believed to be have been of about half European origin and half Middle Eastern origin.
Since the 1970s, many studies have attempted to determine whether common ancestors existed to the present Jewish communities or if the descendants are related instead to the non-Jewish populations where they lived.
Genetic studies on Jews are part of the population genetics discipline and are used to better understand the chronology of migration provided by research in other fields, such as history, archaeology, linguistics, and paleontology.
These studies investigate the origins of various Jewish populations today.
The earlier studies tried to answer this question using "classic" genetic markers (blood groups, enzymes, etc.).
Since the late 1980s and especially since the beginning of the twenty-first century, geneticists have worked on analysis of the Y chromosome (transmitted from father to son), or mitochondrial DNA (transmitted from mother to child), which have the characteristic to be transmitted in full (without recombination).
Jews living in the North African, Italian, and Iberian regions show variable frequencies of admixture with the historical non-Jewish host population along the maternal lines.
In particular, they investigate whether there is a common genetic heritage among various Jewish populations.Studies of autosomal DNA, which look at the entire DNA mixture, show that Jewish populations have tended to form relatively closely related groups in independent communities, with most in a community sharing significant ancestry.Behar and colleagues have remarked on an especially close relationship between Ashkenazi Jews and modern Italians.Ashkenazi Jews are believed to be descended from a group of people who numbered just 350, living 800 years ago.
For populations of the Jewish diaspora, the genetic composition of Ashkenazi, Sephardi, and Mizrahi Jewish populations show a predominant amount of shared Middle Eastern ancestry.According to Behar and colleagues (2010), this is "consistent with the historical formulation theories the Jewish people as descending from ancient Hebrew and Israelites of the Levant" and "the dispersion of the people of ancient Israel throughout the Old World".