There is no gene for homosexuality. In lesbianism, it is overwhelmingly a choice, where many women choose to be with other women for emotional reasons or response to bad relationships with men. For homosexual men, there is a strong biological link - the odds a man will be homosexual are directly related to his number of older brothers. Theory is that the mother's body starts to fight the testosterone and leads to feminized younger sons. However, despite sexual attraction, one can still choose how you live your life.
Given that sexual attraction is partially biological but sexual behavior is a choice, children of homosexuals grow up where the behavior is seen as the norm but biology is TBD.
Per the Regnerus New Family Structure Study (NFSS) study, around 60% of children of lesbian and 70% of children of homosexual men identified as strictly homosexual, versus more than 90% of children of heterosexual couples.
Those who identified as heterosexual had experimented with same sex relationships at a much higher rate than the general population.