On the Window Sill

Here's a biology question. You can find all sorts of information on cat coat colors in genetic texts and online. Tabby vs. plain, white with/without deafness, calico and tortoiseshell, agouti, yellow vs. gray, Persian, etc., etc. Everything but how the tuxedo pattern comes about. Do embryonic melanocytes stop short of the ends of the limbs, belly/chest, chin/lip when they migrate away from the neural crest during development? If so, why? Why do cats often have a black tip to the tail but rarely a white one, when dogs often have both? Do melanocytes somehow pile up at the end of the neural crest to make a black tip on tails? Other domestic animals, have the tuxedo pattern and countershaded wild mammals have a sort of tuxedo pattern. Why do some mammals, e.g. ratel Mellivora capensis have a black belly? What gives here?

That is way out of my area of expertise, although something about developmental timing may be implicated in some of these patterns. This is something that Razib should know better.

Those are two very handsome kitties.
-gfl