Tag Archives | zorse

Tobiano, the “top dog” pattern


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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Thinking zebras… and horses

When you hear hoofbeats, think horses, not zebras

I have been thinking about zebras lately. Part of the reason is probably best left for another post, since it’s a different tangent than this one. As readers of the studio blog know, I tend to wander off on tangents a lot. I do eventually get back to where I was, though it often takes a while. Oddly enough, this will bring us back to Dominant Whites, though a bit indirectly.

The other reason is that I recently ran across my copy of the Penycuik Experiments by Professor James Ewart. The Penycuik Experiments were conducted in the late nineteenth century. I originally found the book when looking for information on the Highland Ponies of Rhum, which are interesting because they are associated with the silver gene as well as the “tiger eye” trait. The text proved to be a dead-end for that, but the experiments described were really cool. I thought it might be fun to share them here, in part because the hybrids are interesting and in part because the experiment itself is a wonderful illustration of just how far we have come in our understanding of genetics in the last 100 years.

Professor Ewart was interested in disproving the theory of telegony, which was the belief that offspring from a cross could be influenced by the traits of the mother’s previous mates. While this might seem quite silly now, at the time the idea was almost universally accepted. Darwin mentions it in The Variation of Animals and Plants under Domestication, citing a case where a mare was crossed on a quagga and later produced horses with striping. The Penycuik Experiment was an attempt to recreate that situation to see if the theory of telegony held. The experiments are particularly interesting in that they predate the re-discovery of Mendel’s work by a few years.

The last quagga died in captivity in 1883, so Ewart used a Burchell Zebra stallion, Matopo. He crossed the Matopo, who is pictured at the top of the post, with a wide variety of mares. Among the first of the hybrid foals was Romulus, from the black Highland mare, Mulatto.

Most of the other hybrids looked much like Romulus – reddish brown ground color with an overlay of black stripes. Ewart also includes photos of the zebra hybrid bred by Lady Meux. In that case a Burchell’s zebra mare was crossed with a “Highland or Shetland Pony” with wall eyes.

He was said to be “light bay”, but in the photos above he looks chestnut. Unlike the other hybrid foals, his daughter does not have particularly visible striping.

She also looks like she might be chestnut, though it is hard to tell from an old black and white photograph. Another zebra hybrid, Birgus, was said to have grown up to be chestnut with black stripes. He was by Matopo and out of a chestnut polo pony mare. Photos of modern zorses suggest that in addition to black striping, the chestnuts also have black lower legs much like a wild bay.

What is interesting is that none of the hybrids in the Penycuik study had white markings of any kind. In addition to the wall-eyed pony stallion, one of the mares used by Ewart was a Clydesdale mare. White patterns can trump the zebra striping, which many have seen with the well-known tobiano zorse Eclypse.

The interesting thing about Romulus, and indeed all the other zebra hybrids, is that they had more stripes than their zebra parent. Ewart counted 43 stripes on Romulus, compared to the five between the shoulder stripe and hindquarter for Matopo. That seems counter-intuitive, that crossing an unstriped animal with a striped one might give the resulting offspring more stripes. That brings me to the other tangent I mentioned earlier. Tomorrow I’ll post about embryonic development and spot frequency, because that’s more really cool stuff.

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