Authors are Anna C Need, Dalia Kasperaviciute, Elizabeth T Cirulli and David B Goldstein. Goldstein authored Jacob's Legacy (click here).
The researchers conclude:
within Americans of European ancestry there is a perfect genetic corollary of Jewish ancestry which, in principle, would permit near perfect genetic inference of Ashkenazi Jewish ancestry. In fact, even subjects with a single Jewish grandparent can be statistically distinguished from those without Jewish ancestry.The team further concludes that in the context of the sample studied:
... it is possible to predict full Ashkenazi Jewish ancestry with 100% sensitivity and 100% specificity, although it should be noted that the exact dividing line between a Jewish and non-Jewish cluster will vary across sample sets which in practice would reduce the accuracy of the prediction.Download the study here, with charts available as separate files. This is a slow download - be patient.
Why this study? The paper indicates that although it was recently shown that genetic distinction between self-identified Ashkenazi Jewish and non-Jewish individuals can be seen in European American genetic patterns, no study had shown how accurate was that self-identified Ashkenazi Jewish ancestry, or the degree of Jewish ancestry among individuals with fewer than four Jewish grandparents.
The random sample included 611 unrelated self-described Caucasian subjects - most in America - who specifically reported whether they had Jewish ancestry, and if so, how many grandparents were Jewish. Each participant was genotyped for some 550,000 polymorphic markers. See the study for the breakdown of the group which included a very tiny minority of Sephardim. Most Jews were Ashkenazi.
The study indicated that every participant with self-reported full Jewish ancestry had a higher score than an individual with no Jewish ancestry. Sephardic participants were only only a few, so results cannot provide information on Sephardic or Mizrachi Jews.
In one paragraph, it appears researchers are not aware of Jewish history or migration - I was surprised that Goldstein did not further explain this quote in the study.
The majority of informative subjects with no Jewish ancestry that scored most highly on PC1 were either of Italian or Eastern Mediterranean descent.To me, it is obvious why these particular participants with "no Jewish ancestry" scored so high. Following the expulsions from Spain (1492), Sicily (1493) and later Portugal, the Jewish population of Sicily was the largest in the world. Following that expulsion, Jews crossed the Straits of Messina into Calabria where the population was estimated as 50% Jewish. I also believe that the term Eastern Mediterranean actually refers to Greece (more specifically Rhodes and Salonika) and Turkey (Istanbul and other cities), which were major destinations for Sephardic Jews following these expulsions.
According to the article, the analysis makes clear that those with full Jewish ancestry are genetically distinct from those having no self-reported Jewish ancestry. Those who self-identified as Jewish and knew their origins were nearly all Ashkenazim. Of the Jewish participants who didn't know whether they were Ashkenazim or Sephardim, but could say where a grandparent had come from, most had Eastern or Central European roots. None had Mediterranean or Middle Eastern ancestry.
Read the complete study at the link above.