Understanding Ashkenazi Jewish Ancestry & Genetics

The history and culture of Ashkenazi Jewish people, the waves of persecution, pogroms, and communal isolation over centuries, help explain the genetic uniqueness of Ashkenazi ancestry and it’s implications on health, 23andMe wrote.

While people of Ashkenazi ancestry have deep roots in eastern and central Europe, their ancestral lines trace back farther to areas in the Middle East. 

But it is in Europe where a drastic reduction in the population’s size and the communal isolation of Ashkenazi people became so profound and created what geneticists call a “population bottleneck”.

Disease, geographic isolation – living on an island, for instance – or migration, or persecution can all create population bottlenecks. That isolation and a sudden decline in the population limit genetic diversity within a group. Over several generations, that can lead to distinct genetic differences and increased incidences of genetic conditions.

Health and Genetics

Understanding this history of isolation helps explain why people with Ashkenazi ancestry are more likely to carry genetic variants that cause certain single-cell recessive Mendelian conditions such as Gaucher disease,  Canavan disease, and Tay-Sachs disease.

In addition, people with Ashkenazi ancestry are more likely to carry so-called “founder variants” in BRCA1 and BRCA2, increasing the risk of breast, ovarian, and prostate cancer.

Tracing the History of Ashkenazi Jewish Ancestry

People of Ashkenazi ancestry first migrated to Southern Europe around 2,000 years ago, coming from Western Asia.

Then – in the Middle Ages – many Jewish people living in southern Europe moved north. They primarily settled in northeastern France and western Germany near the Rhine River. It was there that their distinct religious, cultural, and Ashkenazi Jewish identify formed.

Although Ashkenazi Jewish ancestry is under the umbrella of “European ancestry,” it’s clear from numerous studies that Ashkenazi ancestry are distinct from other European populations.

Ashkenazi Ancestry and Other Jewish Ancestry

While most people with Ashkenazi ancestry trace their DNA to Eastern and Central Europe, they are often more genetically like other Jewish populations – such as Sephardic Jews or Jewish groups with roots in Iran, Iraq, or Syria – than other Europeans.

People with European ancestry are genetically distinct from those of Asian descent. What is less obvious is that genetic variation also exists within European groups.

A Population Bottleneck

What contributed to those differences was the history of the Ashkenazi people. During their long history in Europe, Ashkenazi Jews faced waves of persecution and cultural isolation that, in turn, impacted their genetics.

Starting in the 11th Century during the Christian Crusades, Jews living in primarily northwestern Europe were not just persecuted but, in some communities, massacred. Other communities in England and France, for instance, were expelled.

Fleeing from that violence and persecution, many Ashkenazi Jewish people migrated east to places like present-day Poland and Lithuania. The violence and the plague, which hit Europe in the 14th and 15th Centuries, decimated the Ashkenazi Jewish population.

While the persecution and isolation that created the bottleneck happened in the Middle Ages, the persecution of Jewish people did not end then. In the 20th century, more than six million European Jewish people were systematically murdered in the Holocaust. Many who survived the Holocaust immigrated to the United States and Israel after the war.

Related Articles On FamilyTree.com:

23andMe Adds Ancestry Composition For People Of Ashkenazi Ancestry

Ancestry Discusses AncestryDNA And Jewish Genealogy

Jewish Genealogy Collection Has More Than 1 Million Entries

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