Genetics and history go hand in hand as two sides of a cryptic anthropological coin and your genetic makeup is the enigmatic roadmap of your family’s past, present and future. In fact, it is through genetics that we are able to evaluate mankind’s enduring saga throughout the ages, utilizing new information to adjust and improve life as we know it.
Which brings us to the genetic anomaly turned pivotal discovery of an ancient population endowed with a unique ancestry. This novel example of genetic drift emboldened geneticists and anthropologists alike to mark significant instances in understanding genetics: The Ashkenazi Jews. Originally, this ancient Jewish diaspora group was composed of approximately 350 people who had migrated from the Holy Roman Empire to northern and eastern Europe, even settling as far north as Ireland. The move was not voluntary as the Jewish people were beginning to be cast out of Rome once Christianity settled in as the official national religion. The Siege of Jerusalem in 70 AD marked one of the biggest turning points of Jewish persecution in Rome when the Temple was sacked and robbed of sacred artifacts. The Ashkenazi are an anomaly because scientists discovered evidence of several genetic bottlenecks; which is described as an incidence in which a population is dramatically slashed to extremely small numbers for at least one generation and then quickly increases again. This rapid reduction and then quick turnaround influx results in little to no genetic variation in their population, also called the Founder Affect. The surviving entities of the original population are thus the “Founders” and create a slightly different populace based on their sample of genes, which might not be random. It is important to realize that because this sample is not random the genes will not be an accurate representation of the original population. As a result of this phenomenon, the Ashkenazi Jews shared a very similar genetic makeup and traits.
The Ashkenazi abided by strict religious customs and always married within their faith, a practice called Endogamy.
The limited marital options meant that all of the Ashkenazi Jews were genetically as closely related to each other as fourth or fifth cousins. This close-knit societal breeding created a closed gene pool and eventually would cause a negative impact to future generations. The reasoning for this comes from the detrimental clash of incestuous reproduction: The closer the genetic makeup of the parents, the more likely it is for the offspring to express a recessive disorder, or mutation. Disease-inducing genetic mutations that normally wouldn’t be passed down became the norm and when two parents carry the same mutation it is passed to their offspring. Even if the parents were carriers and unaffected by the disease, two carriers would pass down two copies of the mutation to their children who would manifest the physical disorder. The self-induced genetic isolation created a population of people with numerous susceptibilities to inherited diseases. Today, approximately 1 in 4 of those of Ashkenazi Jewish descent are a carrier for these genetic disorders. DNA testing is highly recommended to those with this ancestry because there is no other way to discern whether someone is a carrier or not and while some of these diseases are treatable, many are life-threatening. A typical screen covers 18 disorders and has significantly decreased the annual number of infant fatalities. Some of the more notable genetic diseases are: Tay-Sachs, Cystic Fibrosis, Gaucher, Blood Syndrome, anemia, and Canavan disease to name a few. Another common Ashkenazi genetic mutation causes a defect in DNA repair which leads to breast-ovarian cancer.
There is a current theory that the Ashkenazi were populated through four major maternal lines. With only four lineages as the source of what is today a population of 10 million, the opportunity to explore the genetic recombination of this religious sect has allured many scientists with advanced studies on Ashkenazi genetics beginning as early as Israel’s declaration of Independence. When Israel was declared it’s own nation in 1948 after the Arab-Israeli war, immigrants from all over the world flocked to the borders and medical exploration was ignited.
One of the most notable doctors was Chaim Sheba who was able to identify different sects of Jews based off of the ailments they were suffering from. One study quotes an admiring associate of Sheba’s stating, “One of my most cherished memories is of ward rounds with Dr. Chaim Sheba at Tel-Hashomer Hospital in 1964. As we passed from bed to bed, Dr. Sheba would say ‘This is a Moroccan Jew. They are particularly susceptible to diseases A and B’ or ‘this is a Yemenite Jew. They are particularly susceptible to diseases C and D.’” Physicians and researchers were finally able to conduct significant studies on this unique group that had previously been dispersed for 2,000 years.
Another theory hatched from this massive return of Jewish peoples to one state, hypothesized that the Ashkenazi Jews are descendants from the mysterious Khazar Empire. The Khazar Empire originated in Central Asia and was a beacon of hope for those who were religiously persecuted in the Middle Ages. The flourishing Khazar Empire was a hotbed of commerce, boasted its own permanent army, and preached tolerance making it a haven for the widely persecuted Jews. This “tolerant” ideology was surprising, as the Khazar Empire was located between the origination of two power house religions: Islam and Christianity, both of which were both applying pressure to convert surrounding communities to their respective faiths. In surprise twist, the Khazar Empire chose Judaism as it’s national religion and thus the theory linking this ancient sanctuary to the Ashkenazi Jews was spawned. However, contrary to this popular myth, it was debunked in 2013 when renowned scientist Itsik Pe’er and his team at Columbia University, studied the genetic makeup of 128 healthy Ashkenazi Jews and compared genetic markers to Flemish people outside of their population for reference. In doing so, they were able to discover and define the genetic code of an Ashkenazi Jew. The Y-chromosomal test showed that the male lineage descended from the Middle East while the mDNA test proved the female genetic makeup was similar to the local inhabitants of Germany and France. To put it simply, during the diaspora the Jewish men migrated north from Israel, converted the women they met to Judaism and married them.
The ancestry of the Ashkenazi Jews is the one of the largest examples of genetic, bottleneck and isolation, thus leading to the Founder Effect. As researchers identify links between mutations and the clusters of diseases these defects cause, we not only glean a better understanding of preventative techniques, but we take one more step to grasping advanced concepts of the entire realm of genetics.
