This post first appeared on October 31, 2011
Another kind of roaning that is often attributed to the sabino gene is the kind seen on this chestnut tobiano pony, Dexter. This has a softer look than the “laced” edges that Dexter’s sabino-tobiano stablemate Splash has.
What makes Dexter unusual, though, is that he has a solid face.
He does have a white patch on one side of his chin which does not reach up to his lower lip, which can just barely be seen in this picture. (Because it is really under his chin it is hard to get a good image.)
It may be that modifiers are suppressing the sabino gene to such an extent that his chin patch is all that is left. It’s also possible that this type of roaning is itself some kind of modifier, and that the white on his chin is unrelated. The commonly accepted rule is that tobiano by itself does not create white on the face, though both myself and others have had reason to question the absolute nature of that rule. (Because that statement is nigh upon heresy to many horse color enthusiasts, elaborating on that probably merits a separate blog post at a later date.)
But it is pretty clear that this is different from true roan. Here is what true roan, when combined with tobiano, looks like. (The photo comes from Reasontobecrazy stock photography.)
Here is a close-up of another roan tobiano.
Notice how the roaning is evenly distributed across the spots. Now compare that to a close-up of Dexter’s hip.
It’s also different from the roan patches that are sometimes seen on tobianos, particularly homozygous tobianos like the one below. Those tend to be rather random, whereas the roaning on horses like Dexter are concentrated around the borders of the dark patches.
Here is a close-up of roughly the same area on Dexter.