Those kohanim whose progeny are to be disqualified from eating terumah will disqualify their mother - according to R. Yosei. The machloket here pertains to how many generations after conversion the newcomers from select nations must wait to be considered full Jews (nations that have less than ideal history with Bnei Yisrael, as it happens). Plus, a very long mishnah of cases of sexual liaisons by kohanim with women that do not permit her to eat from terumah. And a myriad of cases in this vein.