James Shaw wrote:
There are identical twins, one of which is quite normal, the other so psychotic that it had to be institutionalized for it own and others safety. There are identical twins, one with juvenile rheumatoid arthritis, the other quite normal. Explain those situations. You can't because it is not, at this time understood, as is the scenario with gay twins that you describe. There are not answers for everything, at this time. Be patient, and quit believing you have answers when you do not, cannot.
There are answers, if you understand both developmental biology and genetics. While identical twins begin at conception with identical DNA, even during development they begin to demonstrate subtle differences in genetic expression. It is unlikely, IMHO, that homosexuality is the consequence of a single dominant mutation, but probably reflects a range of genes interacting with environmental factors.