there was a foolish attempt in the last part of the previous century to try to prove that homosexuality was genetic, despite the science being abundantly clear that behaviour in mammals is
never genetic. simple organisms, like reptiles and insects, have little ability to undo their instinctual reactivity, but the development of mammal intelligence rendered instinct largely irrelevant. all mammals, from lions to mice, are born helpless and empty and without any residual genetic instincts and need to be taught everything by their parents or community. an earlier era of biology would have argued that predators like tigers and lions are, like crocodiles, born with an instinct to hunt, but we have known for decades now that that is completely wrong and that lions need to be taught to hunt and will starve if they are not taught to hunt by their parents. the
tabula rasa model is the correct model in all mammals and a small subset of birds.
for that reason, citing the gay penguin as biological proof of homosexuality was stupid. birds are still largely instinctual, whereas mammals have essentially no instinctual basis in their behaviour at all. if somebody drops a kid in the forest, they might figure it out, but it will be by self-learning and not by instinct. humans don't have a caveman instinct underneath their civilized exterior. that idea is a debunked myth.
what genes actually do is code for proteins; hormones are proteins. genes make mistakes, and those mistakes have consequences that are usually negative, but they don't directly control or affect choices. the result is that mammals have free will, and that that free will is genetic, in the tabula rasa we're born with, up to the caveat that we don't decide how to manufacture proteins, that is autonomous and determined by our genetics.
it follows that the idea that being gay is genetic is actually incredibly stupid. this is obviously wrong, as the mechanism of using genes to explain sexual behaviour is incoherent. that makes absolutely no sense.
the result of looking for a gay gene - and they looked. hard. - is that they couldn't find one. all of the effort put into finding a gay gene resulted in the demonstrably clear outcome that there is no gay gene and homosexual behaviour is neither biological nor genetic but, rather, a clear individual choice that some people do or don't make. people can choose to be gay, they can choose to be straight, they can choose to be bi, or they can choose to be celibate, which is the actual choice that i've actually made for myself, in my own life.
however, what researchers did find in their attempt to find a biological basis for homosexuality, which they proved wrong, was that there are certain genes that code for testosterone and estrogen development and that errors in transcription in these genes can lead to individuals unable to produce normal amounts of sex hormones. it follows that while homosexuality has no biological basis, it is true that some biological men are born with low testosterone or high estrogen, and that this result can affect their behaviour, in leading to identify with women, or become attracted to men. this generates a biological basis for gender identity that does not exist for homosexuality.
there has recently been a movement amongst conservatives to deny all of this, and flip the evidence over to align with the outcome they want, which conservatives often do, and which is that both gender and sexuality are fixed by god, via the mechanism of genes. the way that these conservatives accept homosexuals is by deciding it's genetic, and therefore determined by god. this might allow them to handle homosexuals as non-deviants (despite their religious rules very explicitly declaring otherwise), but it has no basis in biology or in sociology or even in the mainstream of the pseudo-science we call psychology. it is, in fact, a classic example of conservative anti-intellectualism and right-wing idiocy. but, it follows that if gender and orientation are both fixed, then transgendered people are just confused; the problem is that that's wrong in it's core assumption, and every branch of science states it's wrong.
rather, the sociologists and psychologists are very clear that orientation is not fixed but fluid, and people can and do experience multiple sexual orientations in their lifetime, and are not born with a sexual orientation but rather make choices in what behaviour to engage in throughout their lives, and are free to change their mind as they see fit.
conversely, the biologists are increasingly clear that genetics is at the core of hormonal expression, and that people don't have any real choice in how their hormones are expressed in their genes, or how much of what hormone their body makes endogenously, which has a clear biological effect on their gender identity, although they do have a choice in how they want to react to that.
personally, i discovered i had low testosterone in my late teens when i began feeling experiences of gender dysphoria, and realize this biological fact is almost certainly a consequence of a genetic mutation. this low testosterone resulted in low amounts of body hair and minimal muscle mass, amongst other things. i might have decided to take testosterone injections to address that, but i didn't, and i have the free will to decide how i want to react to my own biology, because i own my own body. that is my choice, not the choice of society, and the law must uphold my right to make choices about my body, whether the society likes it or not.