Tobiano


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.

Here is another horse showing the same kind of softly roan edges,  although he has the white face markings that Dexter lacks. (The photo comes from Citron Vert Stock.)

 

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Christine Sutcliffe shared this guy in the comments section of the previous post, and I wanted to post him here where he’ll be more likely to be seen. He carries the tobiano pattern, as did the others, along with varnish roan (leopard complex) and one or more of the overo patterning genes.

I say that because he has a broad blaze and two blue eyes.

Horses like this one often get misidentified as grey tobianos, especially if the version of their appaloosa pattern lacks spots, or if their tobiano pattern hides the area that would have shown the spots. It is an easy mistake to make, because varnish roans turn whiter over time much like a grey. (I’ve noticed that as my own black near-leopard mare has aged, more people call her a “grey appaloosa”.)

Some greys lose pigment on their faces, which can also confuse the issue. I suspect that is why varnish roan (leopard complex) has remained in some grey breeds (or strains in breeds) even when appaloosa patterns are not considered desirable or are outright banned. If true greys can develop mottled skin with age, then the facial mottling that develops from varnish pattern might not throw up warning flags.

What sets the progressive whitening of varnish roan apart from grey is that it leaves the spots. The dark spots on this fellow’s rump will remain, no matter how much paler his body becomes. It is thought that all appaloosas roan out, sooner or later. That only applies to the body color, though. When grey is added to the mix, it all lightens. The really loud appaloosa Friesian cross Mystic Warrior is a well-known example of this. This link shows his current appearance along with pictures of the loud black leopard he was as a foal.

Because grey eventually erases the spots in a way that varnish roan will not, it is often considered undesirable by appaloosa breeders. Contrast is often the name of the game in breeding for attractive appaloosa patterns, and grey removes it. That’s also why leopards have traditionally been so sought out by breeders; theirs is the pattern that keeps its contrast. Blanket patterns eventually look a lot more like varnish roans over time.

What is interesting about grey and appaloosa, though, is that before it takes the spots away, it tends to skew them. The angled spots on Mystic Warrior show that really well. On appaloosas with dark areas, like those with blanket patterns, it often adds dramatic white spotting that looks like a cross between marbling and dappling. For those that have the most recent edition of the Sponenberg book, there is a part-Arabian with this type of effect. (He is also pictured in the German book Pferde aus Licht und Schatten.)  It seems that not all grey appaloosas get altered in these ways, but it is common enough these are good clues that grey is there.

When it comes to how the different patterns interact, tobiano could be called the top dog. Pretty much no matter what else it gets paired with, the end result still looks pretty much like a tobiano. Sometimes the other patterns add new areas of white, like this tovero here with the bald face and white ear, but visually it is still pretty easy to identify the horse as carrying tobiano.

Here is an pony with both the appaloosa and tobiano patterns. Notice how the white areas from the tobiano just overlay the leopard pattern.

The lighting for that picture was just right to show the tobiano markings. In bright light, it would be possible to miss it. The outline is also lost as the pattern travels up his hindquarter, when it meets what would likely be the pink-skinned area on a leopard.

Here is tobiano overlapping dark-headed frosty roan.

Tobiano even stays intact when inherited by zebra hybrids. (Photo from Wikipedia Commons.)

It is tamped down and made more minimal in donkey crosses, but it is still quite obviously tobiano. (Photo by Amanda Slater.)

Which brings me back to the discussion about white Miniatures from a few days ago. I truly did not think the colt in question was a Dominant White, but rather a tobiano that was rapidly greying out. As a young foal, he looked like a chestnut tobiano. It did lead to the question, though, about what Dominant White might look like paired with tobiano. Would it overlap the pigmented areas (few though they might be in many cases), much like it did with the leopard above? Or would the instructions to make the horse white override the tobiano patterning altogether?

I suspect that the answer lies in the way the two patterns function at the molecular level. I enjoy reading papers about that aspect of genetics, but in many ways that is above my pay grade. As an artist, I am at heart someone who understands the nuances of phenotype (that is, how the horse looks) far more thoroughly than I understand the underlying mechanics. I will need to wait until someone crosses a Dominant White (particularly one of the families that tends towards the “leaky” variety rather than the all-white) with a tobiano to find out.

 

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