Founders and mutants



It is known that the two horses above share a common ancestor. Although most people would not think of a Shetland Pony and an Arabian as being related in any meaningful way, if we could trace their pedigrees back far enough, there would be at least one common name on both sets of papers. That same name would appear on these Percherons’ pedigrees.


They are relatives, too. We know that because all four of these horses are grey. That means that somewhere in the pedigree is the horse – one single horse – that carried the original mutation for greying. That is the founder for the trait, and all grey horses trace back at least once to him or her.

This discovery, made by a research team in Sweden in 2008, made headlines. Around the same time, a similar story about a common ancestor for blue-eyed people also attracted attention. I have heard more than one person express surprise about this, and I think that speaks to a common misunderstanding about horse color. There is an assumption that while most horses get their color from a parent, from time to time color mutations repeat themselves. This leads to the idea that there might be an “Arabian grey” which is different from, say, a “Shetland grey”. Yet in most cases, the mutation is a one time event. What’s more, mutations involve so many variables that even when the same gene is mutated, the results are not necessarily the same.

That is why a patterns like Dominant White and Splash White, which do have multiple versions, require different tests for each. Rather than just scanning across a gene to see if something is different, the test is looking for a specific mutation – the exact change to the genetic code. And that exact change began with the founding animal where the mutation first occurred. Unfortunately, the terms mutation and mutant have a negative connotation. They are often used in a derogatory way, particularly among animal breeders who are talking about what they view as a negative trait. But mutants are simply animals that carry some kind of alteration (mutation), whether that change is good, bad or a mix of the two.

The concept of a founder – the original ‘mutant’ animal – is really helpful for breeders who want to determine what colors or patterns their animals might have. With more recent mutations, often the founder is known either by name or at least by breed. If it is known that the second Splash White mutation (SW2) occurred in one American Quarter Horse family, then it can be ruled out for those breeds that have no conceivable connection to the Quarter Horse, and considered highly unlikely for those Quarter Horses not known to be related to the founder. Although the three splash white tests are currently offered as a set, for the other colors knowing something about the founder can prevent the purchase of unnecessary tests.

Founders are also a fascinating subject for people like me who are interested in breed histories. The older mutations, where the founder lived long before the advent of recorded pedigrees, offer a way to look at how different populations spread and how breeds were developed. In those situations, color is sometimes the most visible marker of the connection between what are now separate groups. In the future, I hope to do a series of posts on what is currently known (or not known!) about the founders of the different colors and patterns. But I wanted to put this concept up for the moment, since it will tie in with a number of upcoming posts.

I’d also like to add a quick administrative note. I want to thank the many people who offer stock images through sites like Flickr, Picassa, and DeviantArt. Today’s images came from CitronVert and The ability to include breeds not typically found in the southeastern United States is invaluable to me, so I am always grateful to those who share their photos either directly (as with the Splash White Project) or through stock photo sites. Your generosity with your intellectual property makes this blog better!

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One Response to Founders and mutants

  1. Elaine December 20, 2013 at 8:11 pm #

    One of the things I think is super interesting about our founding mutants :-) is to consider that when they happened in human timescales, humans made a choice to say, “This is a totally interesting mutant, I want more of these.” One can easily imagine that some of the more remarkable colors would propagate in exactly this way.

    A horse like Justin Morgan may be such a founding mutant. He was different enough from the other horses of his day (or perhaps just well-promoted) that a whole population descends from him because of those unusual qualities. Whether he just had an especially fortunate combination of ordinarily inherited genes or if he actually had an interesting mutation would be an interesting study.

    I’ve really enjoyed some of your other discussions about how a single influential individual can change the color of a breed, whether it was because of or in spite of that unusual color.