The first PC showed a gradient that distinguished “southern” or Mediterranean origin from “northern” European ancestry (Figure 1B). The mean +/− SD of the first PC scores for those individuals with the same (or adjoining for Scandinavian) 4 grandparent (GP) country of origin or 4GP Ashkenazi ancestry information were: Irish (51 individuals), mean −0.022 +/− 0.002; Scandinavian (3 individuals), mean, −0.022 +/− 0.002; United Kingdom (5 individuals), −0.020 +/− 0.002; German (11 individuals), −0.016 +/− 0.004; Spanish (14 individuals), 0.004 +/− 0.003; Italian (28 individuals), 0.015 +/− 0.006; Greek (9 individuals), 0.022 +/- 0.011; and Ashkenazi (38 individuals), 0.045 +/− 0.003. For participants self-identified as of Ashkenazi heritage, but who lacked 4 GP information (234 individuals), the mean PC1 score value was 0.043 +/− 0.008.
