[… it’s important to point out that recruiting twins with different sexualities is extraordinarily difficult. Researchers estimate that just 0.012% of the population consists of a gay or bisexual person who happens to have an identical twin](https://kinseyinstitute.org/news-events/news/2019-07-26-twins-sexual-orientation.php)
As far as we know, it isn’t. There are a few genes which some researchers have suggested are *loosely* associated with what sexual orientation someone will turn out to be, but the correlation is weak and could easily have other explanations. It just seems to be some kind of developmental roulette game.
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