Jewish II is characterized as the “strongest” marker, correlating very often with Ashkenazi Jewish parentage, especially in its double allele form (two checks under parents’ columns on an 18 Marker Ethnic Panel or Jewish DNA Ancestry report). This description is validated by ENFSI results for 22 countries of Europe, where its strongest showings are in Czechoslovakia, Croatia and Slovenia (all Central European Slavic populations).
Its lowest frequency occurs in Germany, Denmark and the Netherlands, countries with few Ashkenazi Jews today. There are no data for Hungary in ENFSI since it does not belong to the European Union. Czech is the closest population in geography and historical composition. Likewise, there are no data for Slovakia, the southern part of the former Czechoslovakia, as Slovakia chose not to participate in ENFSI.
In Czechoslovakia, nearly 1 in 26 people carry Jewish II in its double allelic form, suggesting both parents were Jewish. The lowest frequency of Jewish II occurs in Scotland, where only 1 in 65 have it.
Note that even though most Ashkenazi Jews spoke Yiddish, a Germanic dialect, they were not necessarily German in origin. More likely they belonged to the Slavic peoples. Yiddish is not linguistically descended from Rhinish or Low German but a High German language of convenience adopted by Slavic-speaking Jews during Germany’s medieval Drang nach Osten (Push to the East). Germany itself was considered a predominantly Slavic nation by geographers until the nineteenth century, when it was first unified under the Prussian monarchy.
The reason Jewish II is not detected at a higher level in today’s German population is because of the ethnic cleansing and genocide committed by the Nazi government in the Second World War. For various reasons, Czechoslovakia and Hungary’s Jewish populations, many of them assimilated Jews, survived better than Germany’s.
The best book about German Jewry is probably The Pity of It All, A History of Jews in Germany, 1743-1933, by Amos Elon (Macmillan, 2002), although the author’s approach to Jewish ethnicity is Zionist and doctrinaire.