Tag Archives | splash white

Range of expression for classic splash

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One of the big questions about patterns is the outer limits of their expression. That is, how much or how little white can there be in any given pattern? Some patterns, like those in the W-series (“dominant white”), seem to show a lot of variation both in the extent of the white and the overall look of the pattern. Other patterns have a little more consistency in their expression. Consistency is what makes a pattern like tobiano so much easier for the casual observer to identify. But even relatively consistent patterns do have a range, and individuals that deviate quite dramatically from what might be considered typical. Animals at the extreme ends are particularly interesting because they tell us where the white most likely originates for that pattern, as well as how smaller-effect modifiers (and possibly other patterns) interact with it.

Classic splash – that is, SW1 in its homozygous form – is one of the patterns that is prone to a fairly consistent expression. That was why it was fairly easy to identify the presence of that specific pattern in breeds prior to the advent of genetic tests. Homozygous SW1 horses had a consistent look, and that look was pretty distinctive. Even so, there were horses that fell along the more minimal end of expression, particularly among some of the rustic pony breeds where white markings tended to be minimal or absent altogether. These horses skirted the edge of the loose rules I had for identifying the classic splash pattern: four white legs, some white on the lower body, white on the tail tip, white face, two blue eyes. Some tended to blur the line between what I thought of as a sabino-boosted heterozygous SW1 and other splash-like patterns (what turned out in many cases to be SW2). Testing has now made it easier to determine when horses from that latter group really are carrying SW1, but I did wonder what testing would tell us about how far thea “rules” could be bent – or if they could be broken altogether. Tobiano testing confirmed that pattern’s biggest rule – four white legs – could be broken. I wondered if what I thought of as the biggest rule for homozygous SW1 – two blue eyes – was also negotiable.

So I was thrilled when Pauline Högdahl sent a photo of Stenbydal’s MJ, the Gotland Pony colt pictured in this post. His owner, Emmelie Nilsson, had him tested and he is in fact homozygous for SW1. To date there have been a number of whole-colored (ie., no white markings whatsoever) heterozygous SW1 horses, but this fellow is the most minimal homozygous SW1 that I have encountered.

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He does have white on all four legs, though the marking on the right front is pretty minimal. His tail end is white, and he does have a small patch of white on his belly. 


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But remarkably enough, he does not have blue eyes. He does have a small blue segment in one eye, but the eyes are otherwise dark. So while very white faces and blue eyes are often considered the defining characteristic of a splash white horse, and homozygous SW1 horses display the classic form of the splash white pattern, having two blue eyes is not an absolute, unbreakable rule. 

While Stenbydal’s MJ may answer the question of whether or not homozygous SW1 horses have to have two blue eyes, he poses new questions. What exactly causes a pattern to be so minimal? Is it all random chance? Or is there some genetic component that tamps down the white, just as there are genetic factors that amp it up on some horses? The latter does seem more likely, especially given that minimized patterns tend to run in families. Here is a picture of MJ with his dam, who would presumably be heterozygous for SW1. 

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His sire, Skotte 492, would also carry SW1, but only has a few white hairs on his forehead. He has at least one other tested homozygous SW1 that is quite minimal. That is Ängdalas Spirello. He also has a son, Zidane Zojvide, that has what appears to be a classic pattern but with one dark (or at least primarily dark) eye, but I am not aware of any test results on him. (More photos of Zidane Zojvide as a young horse, where the contrast on his pale palomino coat is a little better, can be seen here.)

This question of factors that suppress patterns, or boost them, ties into some of the new research on white markings. That is a subject I’d like to cover, especially in light of the new paper that was published just recently. To do that, however, I want to give some background on past studies of white markings, including what was already known, and the system that was developed to begin assessing white. Watch for those posts in the upcoming weeks, but I have at least one more splash white post to make first.

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How I learned to stop worrying and love incorrect color terminology

NoBuckskin

Okay, maybe not love – but certainly stop worrying about it.

Like a lot of people who find horse color fascinating, I once spent no small amount of time online, spreading the Gospel of Proper Color Terminology. Surely if I just presented the facts in a convincing manner, I could save the world from people who were convinced they had palomino Arabians!

Fortunately for my own sanity, my career as a parent – begun just a few years after large numbers of horse people discovered the internet – got in the way of my missionary zeal. Toddlers do not recognize the need for uninterrupted bathroom breaks, never mind enough time to compose an extended explanation about why you really should not call your double-diluted cream an albino. Children also raised my threshold for the type of thing that required immediate action. I could live with someone on the internet being wrong; it was not like they had just painted on my bathroom walls with chocolate pudding.

Looking back, though, I see that my enforced absence from online discussions had unexpected benefits. For a researcher there is a significant downside to spending a lot of energy “correcting” wrong information. If you spend too much time telling people that some common misperception is wrong, you run the risk of having that response become automatic.  It makes it a lot harder to reassess your position, because it is a rare person that can argue a position for a long time without getting their ego involved in being proven right. From there, it is easy to overstate your case. “Your flaxen chestnut Arabian is not a palomino” becomes “there have never been palomino Arabians”, which then becomes “Arabians do not carry any dilution genes.”  The first is – or at least to date has been – true. The next statement is actually open for debate, and the last one is incorrect. (See also, here. Similarly diluted Morgans can be found here.)

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And intriguing painting of the early Twentieth Century Turkish Arabian, Übeyyan. How accurate was this portrait? And what color was he?

The other downside to spending a lot of time correcting errors is that if you automatically dismiss something, it is really easy to overlook important information. Even when people are wrong, they may still hold a clue, a piece of the puzzle you are trying to assemble.

I sometimes get asked why I spend so much time with older documents when so much has changed in our understanding of coat color genetics. Why, for instance, spend time translating Valto Klemola’s 1931 paper on “Recessive Pied” when there are papers written just this year and last on what we now call Splashed White? Surely the new information replaces Klemola’s theory about recessive spotting in horses.

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I am sure my husband also wonders why I need books about horse color published in 1912. After twenty years of losing more and more shelf space to them, he has given up asking.

But the fact is that Klemola – and many of the other earlier authors – were not entirely wrong. They were almost always working from a partial picture, but often the piece that they were seeing was not incorrect. It was simply incomplete.  Read with an understanding of the larger picture, what these older researchers have to say can still provide valuable information. The same is true for owners and breeders who may not have the same grounding in the latest scientific theories. They still have the potential to be valuable observers. It is worth being open to what they have to say, without being excessively concerned about the “correctness” of how it is said.

At the moment terminology – particularly the terms we use when talking about white patterns – are in a state of transition. We are struggling with words that do not completely fit our present understanding. I hope to tackle that in more detail in a future post. It is worth remembering, however, that the real reason for adopting a consistent set of terms is so that we may all communicate more clearly with one another. It may take a little more effort, and perhaps a few more words (and patience) than it once did, but that is ultimately the goal.

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New developments

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I think I need to work on final book edits every spring, because it seems to guarantee that a paper will come out within that time period. Animal Genetics has a short communication out with three new KIT mutations and one new PAX3 in horses. There are also two papers out on KIT patterns in dogs, which is new. Before this, the piebald patterns in dogs had been mapped to MITF, which in horses is the other site for splash white. The picture above is the German Shepherd that carried the de novo mutation. (I must give a special thank you to her owner for allowing me to include it here.) I had intended to put together a longer post on this pattern, known as panda, because it touches on the subject of blue eyes in KIT mutations. She obviously has blue eyes, and her owner confirmed for me that some of her descendants have had a blue eye or blue segments in their eyes. This follows the pattern that I have seen in the historical records of some suspected Dominant White horses (also presumed to be KIT mutations). Blue eyes do seem more common in the originators, and then appear to occur sporadically – often in a less pronounced degree – in the descendants. Interestingly enough, the MITF mutations are not associated with blue eyes. In fact, this family of Shepherds was the first instance I noted where blue eyes in dogs were linked with a form of white spotting so I was particularly happy to see the mutation formally identified.

What is interesting about the new equine discoveries is that they really do not fit neatly into existing naming categories. The KIT mutations have been assigned numbers in the “W” series, but at least one appears to be subtle white-booster rather than a true dominant white. I had been urged by a couple of researchers, as I got close to my publication date, to avoid the use of the term “sabino” and just use “white spotting”, and I see now why. I suspect this will become more complicated as time goes on and more mutations are identified. One thing does seem clear, and that is that several of these sites mutate often – apparently in ways both large and small!

Just as I did with the book last year, I’ll be updating the text to reflect this new information for the new full-color supplemental book. I had feared there might not be much new information, but this coupled with some of the things I have been researching in the last few months should make for a lot more content as well as more abundant (and colorful) images!

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