Once considered a radical theory, the idea that white markings are a form of pinto patterning has become widespread.
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.
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?
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.