There probably are other biological factors like hormones, for example, and other variables we simply don't know anything about yet. The study follows others that have suggested a biological influence in sexual orientation, but scientists still cannot explain what makes a person homosexual, heterosexual or bisexual. The latest study does not identify a specific gene. But like Hamer's 1993 study, it suggests such a gene resides in a particular region of the X chromosome, one of the microscopic threadlike structures that carry genes.
Men inherit the X chromosome from their mothers.
Hamer said there was no way to know how strongly the gene influences the development of homosexuality in men. Researchers looked for such an effect in women but found no evidence for it. Mass. Dr. Elliot Gershon, chief of the clinical neurogenetics branch of the National Institute of Mental Health, said the work does not prove such a gene exists in the chromosome segment, but it is suggestive. The study focused on a region of the X chromosome that had been identified by the 1993 study. In a man, this region can get its genetic material from either of his mother's two X-chromosome versions.