Apparently he's 1/4 Jew, but since the Jews have survived as a race by interbreeding with other races, I think it's' a mistake to try to use fractions to measure Jewishness. A single drop = 100%. I'd trust Owen Benjamin if he got himself and his kids sterilized. He names the Jew so he might be able to admit this is a reasonable precaution to protect humanity, but I don't think he'd actually do it.