Maybe, maybe not. Genetics is far more complicated than it's often portrayed as being. My favourte example of that is eye colour. It's quite well studied because it's easy to measure. But nobody even knows how many genes are involved in determining eye colour, let alone which ones or how. So far, 14 are pencilled in and 12 of those do other things as well. It doesn't seem to be a probabilistic thing or to have environmental factors.
Eh? I never claimed it was simple. How does it not seem to be a probabilistic thing - what you're saying makes it more likely that it is... Certainly inheritance of genes is, that's quite a common example in applied probability courses. Look at it another way - if it were completely deterministic then we'd have likely been able to identify a set of gay genes, instead it's probably a fair bit more complicated than that.