There have been many debates as to whether homosexuality is a heritable trait passed down through the genes or parents, or if it is based on an environmental influences. Here I have included some examples to help to put a conclusion to this debate.
One example of homosexuality being considered a genetic disorder takes place within an episode of the animated comedy series, Family Guy. In this episode, Peter wants to make money and is injected with a homosexuality gene for an experiment. Peter appears to become homosexual and looks to the opposite sex as a mating partner. The family doesn't like this new Peter so they send him to a straight camp, which he quickly escapes. But in the episode, Peter's homosexuality wears off and he soon returns to his heterosexual self. Here is a link to the episode on megavideo.com. http://www.megavideo.com/?d=U0O5OS95
But instead of relying on a television series, lets look into some actual studies, specifically twin studies. One of the major studies to date is the Bailey and Pillard study of 1991. They recruited a sample of 161 male homosexual participants, all over the age of 18 with a twin or adoptive brother through advertisements placed in homophile publications in several cities in the Midwest and Southwest of the United States. The co-twins and adoptive brothers were sent questionnaires in which five questions regarding sexual orientation were embedded in over 100 other items regarding social attitudes, personality, and childhood behavior. Their data showed that 52% of monozygotic (identical) co-twins, 22% of dizygotic (fraternal) co-twins, and 11% of adoptive brothers were homosexual. The data regarding co-twins and their homosexuality seem to be moderately correlated, especially compared to the data comparing adoptive brothers and their homosexuality. This data suggests that homosexuality is a result of nature, but that nurture does play some role.