Tuesday, January 31, 2006

Who knows four?

Ashkenazi Jewish Founders Traced
By Rossella Lorenzi, Discovery News

Jan. 27, 2006— Four women who lived 1,000 years ago somewhere in Europe are the ancestral mothers of some 3.5 million Ashkenazi Jews alive today, a genetic study has concluded.
Part of a small group who founded the Ashkenazi Jewish community, each woman left a genetic signature that shows up in their descendants today, Karl Skorecki of the Technion-Israel Institute of Technology in Israel, and colleagues reported in the online edition of the American Journal of Human Genetics.
Estimated at around eight million people, the Ashkenazi Jews account for the majority of the current Jewish population.
The term "Ashkenazi" refers to Jews of mainly central and eastern European ancestry, as opposed to those of Iberian (Sephardic), Near Eastern or North African origin.
"Most historical records indicate that the founding of the Ashkenazi Jewry took place in the Rhine Basin, followed by a dramatic expansion into eastern Europe. However, both the origin and size of the maternal ancestral deme remain obscure," wrote the researchers.
To shed light on the beginnings of this Jewish community, Skorecki's team sampled DNA from more than 11,000 people representing 67 populations.
For each subject, the researchers recorded "the birthplace of their mothers, grandmothers, and, in most cases, great-grandmothers."
Comparative analysis of mitochondrial DNA (mtDNA) — DNA passed down only on the mother's side — showed a mutation which could be traced back to four women.
These ancestral mothers carried "distinct mtDNAs that are virtually absent in other populations," said the researchers.
Non-Ashkenazi Jews also carry low frequencies of these distinct mtDNA types, providing evidence of shared maternal ancestry of Ashkenazi and non-Ashkenazi Jews.
"We conclude that four founding mtDNAs, likely of Near Eastern ancestry, underwent major expansion(s) in Europe within the past millennium," the researchers said.
The European Jews expanded dramatically from 25,000 people in the 13th century to about 10 million just before World War II. The Nazis killed about six million Jews.
Today, the total Ashkenazi population is estimated at around eight million people, while the world Jewish population is about 14.5 million.
"I have seen the paper and it certainly looks interesting. On a first reading it seems to me that the data is consistent with a major founding event," Mark Thomas, of the Center for Genetic Anthropology at the University College London, told Discovery News.
Indeed, previous findings based on studies of the Y-chromosome, which is passed from father to son, have pointed to a pattern of shared paternal ancestry of global Jewish populations, originating in the Near East.
The study is "vital to understanding the mechanisms of genetic health and disease in human populations," said the researchers.
The Ashkenazi Jews are known to display 20 recessive hereditary disorders.


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