In popular thinking, homosexuality is increasingly viewed as a justifiable, even somehow unavoidable, lifestyle, for those biologically predestined for it. One often hears in the media that one's sexual orientation is due to a sort of genetic fate. Below I have excerpted a useful and apropos paragraph from an excellent book I recently read.
"An area of particularly strong public interest is the genetic basis of homosexuality. Evidence from twin studies does in fact support the conclusion that heritable factors play a role in male homosexuality. However, the likelihood that the identical twin of a homosexual male will also be gay is about 20 percent (compared with 2-4 percent of males in the general population), indicating that sexual orientation is genetically influenced but not hardwired by DNA, and that whatever genes are involved represent predispositions, not predeterminations."
In short, homosexuality is the result of many factors: personal choice, upbringing, environment, conditioning. Genetics plays some role in sexual orientation, but it would be false to claim that it is the determining factor.