There are now some 8m people of Ashkenazi origin around the world
Almost half of Europe's Jews are descended from just four women who lived 1,000 years ago, a study says.
Scientists studied the mitochondrial DNA - passed from mother to daughter - of 11,000 women of Ashkenazi Jewish origin living in 67 countries.
The Ashkenazis moved from the Mid-East to Italy and then to Eastern Europe, where their population exploded in the 13th Century, the scientists say.
One of the authors said the study shows the importance of Jewish mothers.
"This I could tell you even without the paper," Dr Doron Behar of the Technion-Israel Institute of Technology told Reuters news agency.
The four women are thought to have lived in the Middle East about 1,000 years ago but they may not have lived anywhere near each other, according to the study published in the American Journal of Human Genetics.
However, they bequeathed genetic signatures to their descendents, which do not appear in non-Jews and are rare in Jews not of Ashkenazi origin.
The Ashkenazis are thought to have travelled from the Middle East to Italy in the first or second Centuries.
In Central and Eastern Europe, many spoke Yiddish - a form of German, mixed with Hebrew.
Ashkenazi comes from an old Hebrew word for Germany.
By the outbreak of World War II, there were some nine million, some two-thirds of whom were killed by the Nazis.
There are now some eight million people of Ashkenazi origin living around the world, the researchers say.
Some 3.5m, or 40%, of them are descended from the four women, they say.