The Ashkenazi Jewish population is a genetic isolate gene pool almost equally close to European and Middle Eastern groups according to a highly detailed genetic study published in Nature Communications on September 9, 2014.
The report is a high-depth analysis of the sequencing of 128 complete genomes of Ashkenazi Jews controls compared with European complete genome samples from 26 Flemish people from Belgium.
Reconstruction of recent Ashkenazi Jewish history from such genetic segments confirms a recent bottleneck of merely 300-400 individuals living in Central Europe, 25-32 generations ago, in the 13th-15th centuries (1200-1400).
This bottleneck was the result of wide spread massacres of Jews in the Rhine Valley during the first three crusades; and additional massacres of Jews who were blamed by European Christians for causing the Bubonic Plague (1328-1351) which killed a third of the population in Europe (and almost half in urban areas).
However, the number of 300-400 Jewish ancestors of today’s European Jewish Population does not mean that only 300-400 Jews survived the Christian massacres. There were several thousand Jews living in Central Europe even after the massacres, but only 300-400 of them are ancestors of the current Jewish population.
First, in every generation at least 2-3% of the population does not reproduce. This results in a steady reduction of the size of the ancestral gene pool, even when the population itself is increasing.
Second, in the 19th century about 100-200,000 Jews married Christians and raised their children as Christians, thus shifting their Jewish genes into the non-Jewish population.
Third, the Nazi driven Holocaust removed almost six million Jewish genomes from the current Jewish ancestral gene pool.
Modeling of ancient histories for Ashkenazi Jews and European populations using their joint allele frequency spectrum determines Ashkenazi Jews to be an almost even admixture of European and likely Middle Eastern origins.
Since the 2.8 million Ashkenazi Jews in Israel are outnumbered by the 3.3 million non Ashkenazi Jews in Israel; the Middle Eastern gene percentage (50-54%) of Ashkenazi Jews will become even larger over the coming generations.