So this means that homosexuality may be caused by a gene, or by some interference during gestation, and most likely can be further developed or inhibited by environment.
I disagree. Furthermore I don't think same-sex attraction can be caused by any one gene. What the experts say is some children exhibit gifts that some incorrectly interpret to imply the child is homosexual. Checkout: How Might Homosexuality Develop? Putting the Pieces Together
Probably much more complicated than any one single cause.
A certain gene might increase the probability 4 fold, while a certain level of hormone A at just the right time or lobe of the brain may increase probability several fold.
You would need a map of all the different factors and still you will likely only come up with a certain set of probabilities. Not to mention that I suspect the causes are not all physical. As much as the GLBT groups don't want to admit it. There is a virtual statistical certainty that some live a GLBT life by choice.
I think you missed the point. Receiving a squirt of testosterone in your brain during gestation is what tells you you are a male, not a gene. If you do not get this squirt of testosterone in your brain during gestation, you brain develops into a female brain.
Now, while this might clearly explain why some children want to have sex change operations, because they do not think they are of the correct gender, by itself it does not explain why individuals with incorrect brain gender assignment would be homosexuals.
Except in the case of animals that are mammals, they are. All of them. All of the time. Animals act based on their brain gender assignment. What their genitals are means nothing compared to what their brains are.
So why should humans be different? To say so, you have to extrapolate an even stranger psychology, what amounts to "male lesbians"; which would be a gender male, but with a female brain, which is itself homosexual, which is why he is attracted to females. This is crapola.
But back to genes. While a gene does not by itself determines sexual brain assignment, it *can*, most definitely, be the switch as to whether that squirt of testosterone is *correctly* given to males, and not to females.
And the resulting squirt of testosterone is all important.