I am about to go pick up 2.2 or 2.3 rat pups today.

I've been doing a lot of research and I have seen a few details about genetic issues but haven't been able to come across a consolidated list of things I should be aware of.

Homozygous Merle is thought to be fatal and the embryo is reabsorbed in the womb - this would naturally lead to smaller litters than if these genes weren't combined. Is this accurate?

Blue x Blue is thought to produce weak or failing pups. Is this accurate? Any more detail?

Rex x Rex makes hairless or patched babies (I realize this isn't a negative trait but I'll pass on that look...)





Any other similar issues like this these that I should be aware of before purchasing?

Thanks.