Currently, it is not clear how sexual orientation is decided. It is possible that there is a genetic component that is inherited from peoples' parents. There should be more research in this issue so that everyone can better understand sexuality. People should not discriminate against homosexuals because of their orientation.
If a child has gay or lesbian parents then I suppose that it is possible that they pass that onto their children, although I am not willing to say it is for sure. If the child idolizes their two parents they are likely going to act just like them, and this may mean that they turn out gay or lesbian as well.
If sexual orientation is not a choice or a lifestyle but is rather a situation which a person realizes is inherent, then it has come to be understood that in many cases there is a genetic component. So if that is true, then it is very possible that there could be a family history of a certain orientation.
I believe it is possible for sexual orientation to run in families. The problem with sexual orientation is the fact that it has been closeted for so many years that we haven't fully studied it due to our religious beliefs. Years from now, researchers will more than likely have through answers to such questions.
Homosexuality is the desire for someone of the same gender as you. It is scientifically impossible for 2 men or 2 women to have a child together. If people with a "gay gene" were born gay they would not have sex (meaning that they couldn't have kids). Thus, if there was a gene for gayness, it would not be passed on. The gene, if it ever existed, would have died out after the first generation. If gayness is a recessive trait, then its increase in the general population would be illogical (real recessive traits like blue eyes have become less common in America over the years). Furthermore if you were born either gay or normal, how could bisexuals be explained? The answer is that homosexuality is not genetic.
No, sexual orientation does not run in families, because homosexual people tend not to have children. Homosexuality is something that just happens to some people. It is like having green eyes. It is something that some people are just given at birth. Some people try very hard to change their sexual orientation and fail.