Jewish populations around the world share more than traditions and laws – they also have a common genetic background. That is the conclusion of the most comprehensive genetic study yet aimed at tracing the ancestry of Jewish people.

In a study of over 200 Jews from cities in three different countries, researchers found that all of them descended from a founding community that lived 2500 years ago in Mesopotamia.

Harry Ostrer of New York University, whose team carried out the study, likens modern Jewish populations to a series of genetic islands spread across the world.

The main reason that Jews continue to form a distinct genetic group, despite their wide dispersal is the exclusivity of the Jewish religion and the tight restrictions it imposes on marriage to those outside the Jewish faith.


Ostrer’s colleague Gil Atzmon of Albert Einstein College of Medicine at Yeshiva University in New York says that the religious traditions and laws shared by practising Jews around the world, and their isolation from their non-Jewish neighbours, means that Jews share many more genomic segments with each other than they do with non-Jewish people.

Marrying out

Jewish law makes it hard for non-Jews to convert. Communities that do accept converts expect them to spend several years studying the traditions and laws of Judaism. Most observant Jews marry other Jews, which limits genetic mixing with other populations, although in the past century some communities have become more accepting of marriage outside the faith.

Atzmon and his colleagues studied the DNA of 237 Jews from New York, Seattle, Athens and Rome, representing Ashkenazi, Turkish, Greek, Italian, Syrian, Iranian and Iraqi groups. They searched for genetic similarities among these populations, and compared them with the DNA of 418 non-Jews.

The study compared 2 million distinct DNA markers known as SNPs spread across the entire genome. That’s four times the number of markers used in previous studies. “We are the first to analyse genome-wide differences,” says Atzmon.

Atzmon’s team found that the SNP markers in genetic segments of 3 million DNA letters or longer were 10 times more likely to be identical among Jews than non-Jews.

Atzmon says that overall, the genetic similarity among Jews is equivalent to what would be expected among fifth cousins from a random population.

Results of the analysis also tally with biblical accounts of the fate of the Jews. Using their DNA analysis, the authors traced the ancestors of all Jews to Persia and Babylon, areas that now form part of Iran and Iraq.

Exiled from Babylon

The genetic tree shows that between 100 and 150 generations ago – the equivalent of 2500 years – the founder population split in two, with half the Jews being dispersed into Europe and North Africa, the other half remaining in the Middle East.

This corresponds with accounts of the expulsion of the Jews into exile in 587 BC by the Babylonian king Nebuchadnezzar.

The genetic analysis shows that amongst modern Jews, the populations that are most genetically similar are those originating from Iraq and Iran. The rest share much more of their DNA with non-Jewish Europeans and North Africans, which may be why many Jews whose recent ancestors lived in Europe or Syria have blond hair or blue eyes.

The team found genetic traces of a period of intense conversion to Judaism during the time of the Roman Empire, when up to 10 per cent of citizens were Jewish. Among modern non-Jewish Europeans, Italians, Sardinians and the French are most closely genetically similar to modern Jews, the team found.

Atzmon says that the analysis could bring medical benefits by helping to identify genetic markers for diseases common in Jewish communities breast cancer, prostate cancer and the inherited metabolic condition, Tay-Sachs disease, which kills in infanthood.

Journal reference: American Journal of Human Genetics, DOI: 10.1016/j.ajhg.2010.04/015