Homosexuality is not genetic at all. Even the sexual hormones in the body do NOT influence sexual preference. I can not stand the way people talk about the reasons that some are gay because they have no idea what they are talking about.
First thing everybody needs to know is there are very few people that are either 100% straight or 100% gay. Most people would say that they have never had a homosexual thought in their life but that does not mean the potential for homosexual behavior is also absent. Sexual humans are attracted to both sexes but usually certain developmental factors makes one voice louder. Loud enough to completely drown out the other voice. Also, your sexuality is decided before you reach the age of 5. Because the sex drive is one of the most primitive physiological functions in the brain and your base physiological makeup is molded before the age of 5, your orientation is decided before you know what sex is. Sexual orientation is decided by a massive list of variables that play in your life when you are very young. Now having said that it is still possible for sexuality be influenced by experiences later in life, but it is not the case for most people.
Sexual orientation has nothing to do with genes at all. Anyone who thinks that is miss informed and has not read enough up human psychology and biology. A lot of people like to ask if it is possible to go from homosexual to heterosexual, the answer is sometimes. Depending on the depth of the established sexuality trying to turns someone sexuality can have sever mental stability consequences.
One more thing. People who think sexuality is a choice are out of their minds. Humans are sexual beings and they want to have sex regardless of what gender they are attracted to. The sex drive is a very powerful function of the human mind. It is what ensured us of being a strong and able race. If the strong drive for sexual activity was not there we would not have evolved like we did. The human sex drive is the largest factor we can thank for the way we are today.