Genetics question

I'm wondering something about horses who are roan + tobiano - are there any horses in the game that display homozygous versions of both (homozygous roan and homozygous tobiano on the same horse)? I tried to search, but it doesn't offer the actual designator (RnT) for roan tobianos, just the backwards one (TRn), which only goes to a handful of glitched horses.

I have never seen a horse in-game that has both of these in the homozygous form, so I'm sort of assuming the answer is no, they don't exist. If someone has one I'd love to see it. If they really don't exist... why not?

Just wondering. I can kinda picture them in my head, seems like they'd look pretty cool. :D

They don't exist because Roan and Tobiano, along with White and Sabino, are all variations of the same gene, called KIT. Since you can only have two copies of a gene (barring a genetic abnormality,) one from each parent, you can only have two versions of KIT. It could be two of the same version of KIT (RnRn or TT) or two different versions of KIT (TSb, RnT, and also Rn+ or T+, + representing the "normal" version of KIT.) You can never have four KIT genes on the same horse, so that is why you can never have a horse that is RnRnTT.

It's just like the various versions of the Agouti gene, A+, A, At, and a. Each horse only gets two copies of that, as well. Of course, the Agouti gene is more about dominant and recessive traits, with one cancelling out the other. The KIT gene variations can overlap, instead of one overpowering the other (except for White, which covers everything.) That makes it confusing because it makes it seem like patterns like Roan and Tobiano are different genes.

However, colors or patterns that are variations of different genes can all exist on the same horse. You can have a horse that is RbRbRnTSpSpO.

Excellent, thank you. I understand most genetics, but KIT is something that causes me some confusion (obviously). Now I know. :)