This research is really old, but it's the first time I've heard about it: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7581447&dopt=Abstract Nat Genet. 1995 Nov;11(3):248-56. Hu S, Pattatucci AM, Patterson C, Li L, Fulker DW, Cherny SS, Kruglyak L, Hamer DH. Laboratory of Biochemistry, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA. We have extended our analysis of the role of the long arm of the X chromosome (Xq28) in sexual orientation by DNA linkage analyses of two newly ascertained series of families that contained either two gay brothers or two lesbian sisters as well as heterosexual siblings. Linkage between the Xq28 markers and sexual orientation was detected for the gay male families but not for the lesbian families or for families that failed to meet defined inclusion criteria for the study of sex-linked sexual orientation. Our results corroborate the previously reported linkage between Xq28 and male homosexuality in selected kinships and suggest that this region contains a locus that influences individual variations in sexual orientation in men but not in women. PMID: 7581447 [PubMed - indexed for MEDLINE] Also see Evidence for a biological influence in male homosexuality. Thank you.