It’s neither trivial nor unnecessary, I’m afraid. Studies have shown that sequences on the same chromosome that are a few hundred kilobases apart sort essentially independently due to crossover, so the base unit here is much smaller than a chromosome, and the chances of the proposed reversion are proportionally much much smaller, though still, as you say, possible.
Simple question Smeghead, does crossing over prevent a child of mixed race parents from ever appearing physically like a pure race individual? If not then it is indeed trivial and an unneccary complication because it goes no way at all towards answering the question.
Of course the base unit is much smaller than a chromosome. If it wasn’t then it wouldn’t be crossingover. That’s the whole point, that it *is[/i[/] just a tiny, short fragment of the entire chromosome. Yes, it occurs, we all accept it occurs. The actual impact is trivial. Yes it can have major impacts, as can wierd events like temporary polyploidy, chimaerism and other oddities but such events are also trivial.
What all these things do is add a totally unnecessary complictaion to the issue that doesn’t go any way towards answering the actual question. I’m afraid that crossing over is trivial given the obvious level of genetics knowledge of the OP. Seriously, this is like launching into a disussion of quantum mechanics and the possibility of spontaneous teleportation when someone asks a question about the probability of a coin toss. Sure it’s true, but all it has managed to do is confuse an issue that is already fairly complicated for the layman.
Since we’re in GQ, I’m going to nit-pick that. We don’t know what “Black Genes” are, or if you can even call something a “Black gene”. So, we don’t know if these hypothetical “Black genes” are dominant or recessive. And, the whole dominant/recessive dichotomy is as oversimplistic when talking about genes as is the White/Black dichotomy when talking about race. And probably for the exact same reason! 
Nearly all of the characteristics involved in black/white differences - skin color, hair type, details of facial structure - do not show a dominant/recessive pattern of inheritance at all, but rather co-dominance: the phenotype of the offspring is intermediate between those of the parents. The only one I can think of offhand that shows dominant/recessive inheritance is eye color, and of course that cannot really be considered a distinguishing feature between blacks and whites since the majority of whites have brown eyes as well.
On top of this, most of the racially distinguishing characteristics are probably multifactorial - influenced by several different genes - further complicating the situation.
You’d think people would be able to figure that out just by looking at mixed race kids. If “Black genes” were dominant, the first generation children of mixed race parents would be as black as their black parent. That’s almost never the case. Yet this “Black genes are dominant” meme lives on in the popular culture. You with the face got it exaclty right-- people think those genes are dominant simply because of the way race is defined in America. It’s circular reasoning at its best (or worst, depending on how you look at it).
There aren’t black genes and white genes. I think we can safely say that. If we
Um, forget the “If we” above.
I know, right? Just because a “biracial” kid is brown and has tightly curly hair does not mean that he takes after his black parent more than his white one. Seems like a real easy concept to understand, but I’ve had to explain this to way too many people–black and white.
T
I have black people in my family that have really dark skin and others that have a lighter skin tone so I know there is not just one “look” but a lighter skinned african american isn’t any less recognizable as being black as a dark skinned african american so what I’m saying is “100%” meaning nobody would look at them (my hypothetical children) and think they were anything but African American and had two African American parents as opposed to a “mixed set” of parents.
I hope you got that. 
I feel smarter after just reading these responses :).
I understand what you’re saying, but the problem with that is that it is totally subjective. Someone who looks “100% black” to one person, may look mixed to another. It all depends on how your eyes are racially calibrated. Without knowing what your dad looks like, we have no idea where he sits on the spectrum (let alone your hypothetical wife’s black half), and so we can’t really say what you or your kids will look like.
Like John Mace suggested, most West Africans would probably think hardly any African-Americans look 100% black. And on the opposite extreme, whites would probably be more apt to see a black person as being “100% black”, even if to your eye they looked “mixed”.
Personally, I don’t put a whole lot of stock in the whole “biracial” notion because I’ve seen so many “biracials” that look no different from the “100% blacks”. In terms of phenotype, it really is a distinction without a difference.