Based on a sample of 2000+ college students and people found in internet chat rooms, the authors of this paper found that gay men and lesbians exhibited low and high incidences, respectively, of A blood type compared to heterosexuals (p < 0.05). Additionally, they found that a unusually high proportion of homosexuals of both sexes were Rh- (i.e. had no Rhesus D antigen on their red cells) compared to heterosexuals (p < 0.06). Blood type and Rh factor were self-reported, and the internet chat room sampling sounds sort of sketchy. If the stats hold, since blood type and Rh factor are genetically determined, there might be some kind of genetic linkage thing going on with sexual orientation. Zip zap.