No, I haven't actually calculated the odds. I wouldn't really have much of an idea how. (I could probably work it out on a basis of - if a gene has x% chance of preventing descendants as compared to not having that gene and a y% chance of being passed on to any descendants - and then do some overly-simplified calculations from the values of x and y - but I haven't, yet.)

Also remember that nothing is perfectly neutral. Even the banana man might get fed banana-cake by a dastardly enemy.

True, but his problem there isn't the banana gene. His problem there is that he has a dastardly enemy. If he didn't have the banana gene, the dastardly enemy could simply feed him arsenic cake instead, or just shoot him.