Chances of chimera hatching?

[pars]

I was just wondering, what exactly are the chances of chimera hatching?

 

[Tye]

Very rare. Like very, very rare.
To get that color pattern you need to have a mutation in the axolotl during development for the genes that control color expression. It's being debated on if "chimeras" actually exist in the axolotl or if they're mosaic axolotls with a specific color expression. What ends up happening in these animals is that the genes that code for one color over the other get mixed throughout the cells in the animal. So some will contain genes and express white while others contain and express the wild-type coloration. It is random and cannot be replicated through breeding, unlike other color morphs. I want to say it's similar to how calico cats work, but that colorization works differently than this one, but for the sake of explanation they're kinda similar looks wise. (the control of coat/fur color is really complex and I'm not sure if the genes for axolotl coloration are even on the same chromosomes as mammals.)
For a true chimera there needs to be a fusing of two or more fertilized eggs during development. The eggs combine into one organism and sometimes contain multiple sets of DNA. I'm not sure if amphibians can be true chimeras or not, I've taken genetics but it was focused mostly on the human side or working with fruitflies. We didn't go into much detail for other animals, or plants for that matter.
The argument for chimeras being actual chimeras is that the color expression is split so evenly down the middle, which suggests a fusion. And some claim that one half will grow at a different rate than the other. But on the flip side, the color expression could just have been segregated evenly down the middle of the animal.
The point is, it's a random mutation or fusion during development and not something you can breed for. The chances are extremely rare, like one site put the chance as a .00001%. I'm not sure where they got that info they don't have sources next to their information for that one. The animals displaying these unique patterns are often infertile as well.
Genetics is weird and complex and wonderful and I know I haven't even scratched the surface of what's out there. If anyone else wants to try to break it down in more detail go ahead, or if there's a more credible probability chance that you know of that would be neat too. (and also if I'm wrong jump in haha. one semester of genetics does not an expert make)