Tag Archives | face markings

Markings are all just minimal patterns, right?

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In 1989, a horse I was riding lost his footing along a steep incline. The fall broke my wrist and shattered my humerus from elbow to shoulder. I was fortunate to have an employer that provided temporary disability, but confining a technical illustrator to a traction bed without the use of her dominant hand for several months is particularly cruel. A friend took pity on me, and suggested that I get a modem for my computer so that I could “chat” – one-handed, hunt-and-peck style – with people on the local computer “bulletin boards”. So by accident, I became an early adopter of online communication. Mostly I got to talk to young, nerdy guys about gaming (the old-fashioned kind, with polyhedral dice and character sheets) and computers. It would be three more years before the technology matured and spread enough that I could find people to talk about what I really loved, which was horses. Horses and their colors! Once that was possible, I filled countless hours chattering on that subject. (Some things do not change.)

One of my favorite topics at that time was pinto patterning, or more specifically, sabino patterning. Crop-out pintos were the focus of a lot of attention, and a number of articles and papers about “overo patterns” appeared around that time. I had also acquired complete, or nearly complete, sets of Walking Horse and Welsh Pony stud books, both of which included very detailed descriptions of markings. I began assembling data, using a numerical grading system based on the amount of white, trying to see if I could figure out why some horses ended up body-spotted. I became convinced that pinto patterns did not just pop up unexpectedly. I believed that the way we were looking at markings and patterns was mistaken, and that the horse world had drawn an artificial line between “pinto” and “not-pinto” – one that probably did not reflect the underlying genetics. Horses like the one below were universally recognized as pintos, but I was pretty sure you could take a lot of that white off and still have something that was genetically a pinto of some kind.

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I was so taken with this idea that I spent a lot of time online suggesting that maybe what we saw as markings were just part of a continuum that ended with a white horse. “Minimal” sabinos might look like an ordinary horse with ordinary markings. “Maximum” sabinos might be entirely white.

Having read a lot more papers (including some that others have kindly translated for me from their original Dutch or German), I know now that what I was suggesting was hardly new under the sun. Others had come to similar conclusions over the years. But it was rather unconventional thinking among horsemen at the time I began writing, and I got the message quite clearly from some that perhaps I was a little touched in the head. (I am sure that being overly enthusiastic about color, and sure of what I knew in a way that only seems to happen when you are twenty-something, did not help!)

At one point, in one of these online conversations, an older and more experienced horseman well-versed in Thoroughbreds finally asked, “Are you saying that all markings are really just patterns, minimally expressed?!” His implication was clear: this was crazy talk. I had not actually entertained that idea, but I had wanted people to consider that markings might occasionally work like a continuum. But his comment did make me think. Could that actually be true? Was it possible that all white markings were just minimal expressions of one of the patterns? I did not think that was the case even then, but it was an intriguing question that stuck with me over the years.

Nowadays, the concept of “minimum” and “maximum” patterns is pretty widely accepted. What I find interesting, however, is that taking that idea to its most extreme conclusion – that all white on the face and legs represent some minimum pattern – is also very widespread. What was once used to illustrate how ridiculous an idea might be, now has a certain following. In fact, if you spend enough time in forums and blog comments, you will soon find this “fact” being used as a verbal cudgel against someone “uninformed” about patterns. It seems we have come full circle in the world of online horse color discussions.

So is that the case? Are all white markings just patterns? Always?

The answer depends somewhat on how you want to define “pattern.” In genetics, piebald and “marked with white” are synonymous terms. Most horsemen, however, see a significant difference between a pattern (ie., something that may extend the white past acceptable or desirable levels) and markings (ie., something that will not extend past the extremities). Because that distinction can have serious implications in many breeds, perhaps putting it in those terms is most helpful. Does every horse with white on the legs or face have the potential to produce something body-spotted?

Or are there genes that, at their maximum expression, never extend past the lines that generally qualify  a horse in a pinto registry? Is is possible to produce this much white, say, and no more?

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What if it never goes even that far? What if you have a breed population where a horse like this represents the maximum end of the white patterning, even counting factors like base color?

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And it does look like there are marking genes that do not, in themselves, produce pinto patterns. The assumption in the literature has been that there is a gene – or genes – that controls face and leg markings. The most current study was done in the Franches-Montagne breed, and was published in 2008 (the link will take you to the full article).  After analyzing 23,019 horses, the study found that:

Our data support the segregation of a recessive single gene accounting for 20–80% of the total heritability for the traits under study (head, forelimbs, and hindlimbs markings).

Our association analysis indicated that the putative major gene for white markings is located at or near the KIT locus. However, further studies are necessary to prove that the KIT gene indeed is the putative major gene for white markings. Our association analysis indicated that the putative major gene for white markings is located at or near the KIT locus. However, further studies are necessary to prove that the KIT gene indeed is the putative major gene for white markings.

This and the earlier Woolf studies on Arabians confirm what I have seen over the years while looking for body-spotted sabinos. Like the splash-like horses that never seemed to pan out when it came to what I was looking for (what turned out to be the homozygous SW1 pattern), not all families or breeds with markings pan out when looking for body spots. In fact, some families that consistently produce what most would call sabino face and leg markings only rarely produce body-spotting, and then often just a bit of white on the belly. This phenomenon was noted by Dutch researchers looking at sabino in their breeds, too. In my book, I referred to that particular pattern as “Flashy White Sabino”. I have wondered if whatever causes this type of pattern is simply interacting with (boosting) the marking gene proposed by the team that investigated the Franches-Montagne horses.

But the fact is that while it is commonly accepted among researchers that there is a separate “marking gene”, we do not have a clear picture of the relationship between those markings and patterns. We do have much better tools now, not only with a wider arrange of genetic tests, but also online databases that pair photos and marking diagrams with entries. Just this past week I was combing through one of those resources in hopes of unlocking some mysteries about a breed that consistently has extensive face white without leg white. But the time investment in this kind of research is huge, especially when the pay-off is just clues. Lab work would still be required to get final answers. Until more work is done, though, absolute statements about what is “always” or “never” true should be treated with appropriate skepticism.

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Requested images

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One of the commenters asked for images of the other side of this horse, which appeared in the original tobiano marking post. I was fortunate to get quite a few good images of him. (If only all the classes were held in this particular arena, which is situated just right relative to the morning sun!)

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You can almost see the random roan patch on his left hip in the side shot, but it is more visible in this one taken from behind.



I liked the way his tail was variegated, so I got a number of shots of it. (Be warned, however, that because Paint Horses can use tail switches, colors on tails may not always be natural to that horse.)

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This was a good shot for showing how the color on the head of a tobiano spreads downward towards the jaw, so that in individuals with more white, there is a narrow “V” at the throat where the color on the two sides merge. I am working on a post that goes into more detail about this, and about how color tends to travel on the faces of tobianos, since that is relevant to the discussion on tobiano face white.

I am also trying to pull together some pieces to expand on some of the unusual colors that have appeared in recent posts. I apologize that we have wandered off in several different directions, but threads tend to come back around eventually. Fortunately you are all pretty tolerant when we take the more erratic, meandering path!

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More on face white and tobianos

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My previous post about white on the faces of tobianos, made before I left for a trip to Boise, generated a lot of discussion both here and on the Equine Tapestry Facebook page. I thought it might be helpful to expand a little on the subject.

Before researchers had the ability to examine color mutations at the molecular level, what we had was analysis of phenotype (how the individual horse looked) and production records. In older articles on color genetics, those were the tools that were used. Analysis of phenotype is still very popular among people who discuss color on the internet, but the appearance of an individual horse – or even just that horse and his parents – only tells part of the story. Extended production records are needed to get a more complete picture. These can show patterns of inheritance across a broad portion of the population, and that can give clues about the nature of the colors and patterns involved.

Looking at these broad trends requires a lot of data, and one of the biggest limitations is that the kind of information needed is not always retained, or if it is, it is not always easy to access. When I wrote an article in 1997 speculating that some horses being identified as dominant white might actually be “maximum” sabinos, it was because I had noticed trends in the early Walking Horse stud books. Unlike many other books from that time, the entries there listed markings (and eye and point color) in detail. Perhaps even more important, at the time was doing the research behind the article, I lived a short distance from the registry where I was given access to records and archived materials. With extensive family records for hundreds of white-born Walking Horses, I was a lot more confident that what I was seeing was a form of sabino.

On one of my visits to the registry, I ran into a breeder doing research on what would eventually be known as the champagne dilution. In the course of explaining what I was there to find, I mentioned that the phenomenon of white foals did not seem to occur in Clydesdales, even though they were uniformly sabino and many of the patterns looked quite similar to those on Walking Horses. The breeder asked if I had Clydesdales, too. When I explained that I just had an aged Walking Horse and a small pony of unknown origins, she expressed confusion about why I had a set of Clydesdale stud books. The reason was that in the pre-internet era, stud books were one of the few ways to obtain information on whole families of horses. Each breed, and therefor each set of stud books, offered a different “control group” to study different patterns. If Clydesdales, for instance, could be assumed to have sabino but not to have frame, then all the patterns in the breed represented what was possible with sabino alone.* In Paints, where frame was common, the possibility that frame was influencing the pattern was always there so until tests were developed it could not be ruled out as causing white on any given horse.

These control groups were not perfect, since the records could contain errors or omissions, but it did make it possible to identify trends. It might not be possible to prove something, but it could suggest useful avenues for testing ideas.

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So what does this have to do with white on the faces of tobianos? Well, the suspicion that some tobianos had face white unrelated to sabino, splash or frame came because it was happening in breeds that were my most reliable control groups for “pure tobiano” because the solid members rarely had white markings of any kind. These were Old World breeds with long-closed stud books, so frame was not likely to be present. Sabino (as we currently understand it) did not appear to be present, and my hope for proof that splash was involved was coming up empty. Why then did so many tobianos have white faces? Why were quite a few quite oddly marked on the face, or blue-eyed? Was it not a coincidence that so many homozygous tobianos – in all breeds – had white faces?

Unfortunately for those of us who live in the United States, it is harder to gather information directly because most of our breeds have markings of some kind, and sabinos of all types are extremely common. The horses in this post, and the horse in the previous post, are all American Paint Horses. Finding a Paint Horse that looks “pure for tobiano” is difficult, and even then it is quite possible that he carries the gene (or genes) for ordinary markings. Those are currently believed to be caused by a recessive mutation to the KIT gene.

That means that this guy, who appears to have only tobiano and no significant white on the face, might carry that mutation and produce offspring that have white on the face.

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What was intriguing was not just that white faces seemed to appear on these tobiano ponies, but that an increase in white on the face of the tobianos did not seem to translate into an increase of white on the non-tobianos. That is what might be expected if the tobianos had a separate mutation creating white markings, either the previously proposed KIT mutation or something new. Were they separate but linked? Or was it simply a part of the pattern itself? Was it both, and if so which forms were caused by each?

Or was I misreading the situation based on limited data? What role was selection, both by breeders and by owners, playing in this?

That is why I found the situation with the Polish Hucul so interesting. Because there are conflicting interests, and because patterns can often create strong opinions on the part of breeders, it is hard to know how to weigh claims that the presence of markings on the tobianos threatens the unmarked nature of the solid population. But the question about whether white on the face might be intrinsic to the pattern is a valid one, as is the question about whether or not an existing KIT mutation (like tobiano) predisposes the resulting foals to new (de novo) KIT mutations that add further white. These questions also tie into the larger questions about the nature of white markings and their relationship to the different white patterns.

* Sabino is now understood as a category of patterns, rather than the one pattern it was believed to be then.

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