Clearly if you are gay, there are differences in your DNA, compared to a straight person. The result is your gayness is that the effect of your genes were emphasised by enviromental factors (how you were raised, experiences), and if the gene-enviroment interaction reached a certain level, you became gay.
So if you have "gay genes but no experiences" you have a small chance of becoming gay, and similarly if you have "gay experiences" but no "gay genes" that doest necessarily result in homosexualty either. Its not genes vs enviroment its genes and enviroment.
Well to answer the question, you can a have a predispositon to become gay when you were born, but that doesnt mean this genetic predispositon
always translates into homosexualty.