Home truth - there is no such thing as “settled science”. This is to neither defend nor oppose the possibility of a “gay gene”, there is simply insufficient information to make a value judgment.
But empirically, would not have simple statistics have shown a tendency toward homosexual behavior appearing at a greater or lesser degree in specific family lines? This has not been proven, and to my knowledge, there has not ever been a serious study done one way or the other.
Nor has study of what is known of the human genome ever shown up an identifiable set of characteristics that even indicate a tendency. Like many human behaviors, homosexuality is a LEARNED trait, resulting from a choice that the individual, rightly or wrongly, made at perhaps a very early age, and often on the basis of incomplete information.
I'd argue that "choice" may not be the right word. Put bluntly, old homos, troll for young uninitiated victims. So at the very least there is some heavy coercion.