Originally Posted by MacabreMikolaj View Post
Thanks guys. It's just so annoying how UC Davis makes it sound like tobiano alone can cause blue eyes. They should be a depedable source, not spreading more misinformation.
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UC Davis makes it sound like tobiano can cause blue eyes because they DO believe tobiano can cause blue eyes. They also believe it can cause excessive face white, especially in the homozygous form.
From Samantha Brooks who was part of the tobiano research group
Tobiano does not, in general cause additional face white. However, like any biological system, if you try to make hard and fast rules mother nature will defy you! Especially in homozygous tobianos, you can see additional face white, broad blazes, blue eyes etc. This is only due to the tobiano...It does not, in general, cause the broad bonnet faces you see in overo horses.
I asked a few more question for clarification and this is what I got back
The key is that some homozygous TO horses will have more white and sometimes blue eyes, but not always (and I could more accurately say "not often".) TO is capable of producing the odd blue eye or two without the aid of overo or sabino genes.
From another researcher on the same/similar topic
The truth is that white patterns are notoriously unpredictable. They do what they want to do, and we can't use the white on a horse to say for sure what patterns they must carry. We know what the tendency of these patterns are, and so we can make guesses, but I would never say that a horse was "definitely" more than tobiano just because it had a star on its face. White patterns are caused by the migration of melanocytes, and it is always possible that they will migrate to a small area outside the "norm."
I, however, do NOT believe tobiano causes blue eyes. The research is old, way back before we had confirmed splash genes, etc etc. They believe that it can because some of the horses in their research had excessive face white and blue eyes and were homozygous. But keep in mind that they couldn't rule out splash, and we know how minimal it can be now, and they didn't have ANY sabinos mapped ( as far as face white goes.)