I should quantify “rarely”.
About 10%.
So if expectation is 100 androphillic men in a random sample, about 110 would be androphillic if the sample all had one of a number of identified candidate genes.
So no, there is no definitive “gay gene” any more than there is a definitive “left handed gene”. Just some genes that bias the odds of atypical neural development. As with left-handedness, it’s congenital.

Zoe,
There’s no reason to take Garcia-Falgueras and Swaab as the bible. We must distinguish the parts that have been observed or experimentally proven from other parts which are completely speculative
The basic idea: Gender identity and sexual orientation of men stem from a “masculinization” of the male brain in utero.
1. Scientists can perhaps observe some changes in the brain after testosterone influence. But what have they observed at all? And isn’t it a bit too quick to call those changes “masculinization”?
2. You can’t observe gender identity and sexual orientation in utero. You can observe them some ten years later. Where are the long-time studies which might confirm a cause-effect relation?
3. Gender identity and sexual orientation can differ. So you wouldn’t have the two stages of masculinization (body – brain) Garcia-Falgueras and Swaab are maintaining, but three stages at least.
4. Nobody denies that effeminate boys are, to a degree, innately effeminate. And effeminate boys become more often gay men. But that development can happen after birth as well as before it.

inca nitta wrote

No science have come to conclusion that homosexual orientation is genetic, actually, APA and AMA, have stated quite the opposite.

Nope.
There are a multitude of factors. Genetics plays a (minor) role, making the neural development more or less susceptible to hormonal anomalies in the womb. Environment also plays a (minor) role in some borderline cases, leading to a slightly greater or lesser degree of bisexuality, especially in women.
But the overwhelming important effect appears to be hormonal environment in the womb. Most cases appear to have no measurable genetic or post-natal environmental component.
So Genetic? Sometimes, rarely. Congenital? Always.
A citation:
Sexual Hormones and the Brain: An Essential Alliance for Sexual Identity and Sexual Orientation Garcia-Falgueras A, Swaab DF Endocr Dev. 2010;17:22-35
The fetal brain develops during the intrauterine period in the male direction through a direct action of testosterone on the developing nerve cells, or in the female direction through the absence of this hormone surge. In this way, our gender identity (the conviction of belonging to the male or female gender) and sexual orientation are programmed or organized into our brain structures when we are still in the womb. However, since sexual differentiation of the genitals takes place in the first two months of pregnancy and sexual differentiation of the brain starts in the second half of pregnancy, these two processes can be influenced independently, which may result in extreme cases in trans-sexuality. This also means that in the event of ambiguous sex at birth, the degree of masculinization of the genitals may not reflect the degree of masculinization of the brain. There is no indication that social environment after birth has an effect on gender identity or sexual orientation.

Genetics is only one small part of it. There’s no “gay gene,” just like there’s no “left-handed gene.” That’s not how genetics works. We have functioning genotypes that are affected in utero as well as during conception.

Biology does not directly mean genetics, at all. These scientific organizations have never made a claim that sexual orientations, be they homosexual, heterosexual, or bisexual, are genetic, ie people are “born that way.”

Actually, Genetics *IS* a part of Biology. Heck, it’s even a part of the “Biology Portal” on Wikipedia! Since Biology is the study of life and how it develops, genetics is not only a logical but a very important part of it.
To wit: “Biology, from the Greek words bios (life) and the suffix -logy (study of), is a branch of science concerned with the characteristics and behaviors of organisms, how species and individuals come into existence, and the interactions they have with each other and with their environment.”
What organziations DON’T say is that pscyhological upbringing, in the mold of outdated Freudian techniques used by Doyle Cohen and NARTH are a likely or even *possible* cause of sexual orientation development.
Why is it so important to you that homosexuality be “curable” that you’d twist facts and misstate things repeatedly to make your point?

Biology does not directly mean genetics, at all. These scientific organizations have never made a claim that sexual orientations, be they homosexual, heterosexual, or bisexual, are genetic, ie people are “born that way.” I don’t find it threatening that biology, among other factors, play a role in having some people embracing a gay identity. It does not prove at all, that a person born with a certain trait, let’s say: small forehead, will necessary embrace a gay or straight identity in the future. But, I find that many avowed gays find it threatening that scientists have not yet and come up, and probably never will, with an irrefutable discovery that homosexuality is genetic, meaning they are who they are because they are “born that way.”