For all intents and purposes, “the fifth line” was a code for asking whether one was Jewish or not. (People of other nationalities, like Tatars and Armenians, against whom there were prejudices and persecution—though not nearly on the same scale as against the Jews—were also picked up this way.) My “fifth line” said that I was Russian, but my last name—which was my father’s last name, and clearly sounded Jewish—gave me away.
Even if I hadn’t been using my father’s last name, my Jewish origin would have been picked up by the admissions committee anyway, because the application form specifically asked for the full names of both parents. Those full names included patronymic names, that is, the first names of the grandparents of the applicant. My father’s patronymic name was Joseph, clearly Jewish, so this was another way to find out (if his last name weren’t so obviously Jewish). The system was set up in such a way that it would pick up those who were at least one-quarter Jewish and everyone of those was classified as a Jew, much like it was in Nazi Germany.