According to Wikipedia (I know, I know Kyu, but there are some nice sources), there is still some debate about whether it is genetic or not. A lot of work is being done in chromosome linking (comparing chromosomes) with gay brothers and their families, and a correlation is apparently present.
I suggest watching John Barrowman's docu-thingy called "The Making of Me" where he meets up with a load of people attempting to explain homosexuality biologically.
I suggest watching John Barrowman's docu-thingy called "The Making of Me" where he meets up with a load of people attempting to explain homosexuality biologically.