An elderly Finnhorse, descendent of the stallion Eversti
In the previous post about founders, I talked about the search for the origins of the silver dilution. I wanted to present another case study that highlights some of the challenges in tracing color lines, this time with classic splash white (SW1). We tend to talk about this form of splash white as being incompletely dominant, with the heterozygous horses tending to show very little white and the homozygous horses having the more distinctive “classic” form of the pattern. When the pattern was first described in 1931, however, it was called Recessive Pied. This was in contrast with Dominant Pied, which we now call tobiano. Later the author, Valto Klemola, proposed changing Dominant and Recessive Pied to “Piebald” and “Splashed White” respectively.
By visiting the Splashed White Project page, and clicking on the button to display heterozygous SW1 horses, it is easy to see why Klemola would have considered the pattern recessive; the horses in that group do not look like pintos. In fact, there is a growing understanding that in breeds with minimal white markings, horses can carry the SW1 mutation without showing unusual – or sometimes any – white or blue eyes. With that reality in mind, classic splash behaves enough like a recessive that it illustrates how the search for a founder is different when the color is not visible in the carriers.
Klemola noted how the pattern sometimes surprised breeders.
In the native breeds of Northern Europe what at first glance looks like a piebald foal may be produced from quite normally-colored parents. This surprising phenomenon has given rise to many fantastic explanations among the breeders…
That observation comes from the second paper, published in the Journal of Heredity in 1933. The earlier paper, published in Zeitschrift für Züchtung, included pictures of Danish and Swedish horses with the classic splash pattern. But the main focus was on the Finnhorse stallion Eversti, who was known for producing both blue eyes and occasional pinto patterns. Although he was only mentioned in passing in the 1933 paper, the earlier one provided extensive details about both his ancestors and his descendants, all of which point to the likelihood that he was heterozygous for SW1. Eversti was a black horse with white markings, but his paternal great-granddam was a blue-eyed pinto (“glasäugig und bunt”). When dealing with historical records, SW1 horses are rarely identified as pintos unless they are homozygous. Had the color been unique to Finnhorses, she could not have been the founder. One truth about recessive colors is that the founder would not actually be the new color. Remember each specific mutation is a one-time event. To display a recessive trait, an animal must be homozygous – it must have two of the same mutation. So even if his pinto great-grandmother had been the first known splashed white, she could have been ruled out as the actual founder. The real founder appears somewhere on both sides of her pedigree, and he or she was probably quite unremarkable. The original mutation could spread pretty far before two descendants were crossed, and the result was a very obvious pinto.
Klemola knew that splashed white was not unique to the Finnhorse, so that unnamed pinto mare was never considered as the founder. As he noted, the same pattern occurred in other Northern European breeds, so the original mutation happened before those breeding groups separated. In more recent times, the same type of pattern was observed in breeds as diverse as the Pasos of Puerto Rico and the Marwaris of India. When a pattern is found across a broad range of breeds and regions, that usually means that the mutation is old. Like other old mutations – silver, tobiano, leopard complex – it is unlikely that much will ever been known about the horse that carried that first SW1 mutation.
Oregon Ice On Fire, a descendant of the Morgan mare Royal-Glo, is heterozygous for SW1
The most that may be possible is to identify some of the sources for the pattern within some of the modern breeds. Now that a test is available for the pattern, carriers can be identified even when they have not produced the more obvious classic pattern. With enough testing information, lines that carry SW1 can be identified. This process has already started in the Morgan breed, where Royal-Glo and Lady In Lace, and ultimately their ancestor Rhythm Lovely Lady, have been named as likely sources. It may be possible from there to connect those horses to some of the early American lines that predated the stud books, since some of those were noted for producing blue eyes. This is perhaps as far back as it may be possible to go with the history of the pattern in America.
In the case of the Finnhorse, Eversti proved to be an influential stallion. His great-great-grandson, Murto, is one of the four male lines in the breed. Both Murto and his son, Eri-Aaroni, were chestnuts with flashy white markings. Intiaani, the first Finnhorse that tested positive for one copy of SW1, carried 21 lines to Murto through the female side of her pedigree alone. Eleven of those were though Eri-Aaroni. And yet that influence is probably the best argument against the color coming from Murto. It is difficult to find a modern Finnhorse without multiple lines to Murto – and by extension, to Eversti. If Murto carried SW1, breeders should have started to see classic splash offspring among his linebred descendants. Yet until the results came back from Intiaani’s test, it was widely assumed that the pattern could no longer be found in Finnhorses. That would suggest that the source for the mutation came through one of the less common lines to Eversti, or even one of the other lines that go back to Eversti’s sire Jalo (grandson of the blue-eyed pinto mare). The flashy white on Murto and Eri-Aaroni may well be unrelated to SW1.
There are quite a few horses that have either tested positive for a single copy of SW1, or that have produced the classic pattern, that look like Eri-Aaroni (pictured above). A fair number of the known splash white producers in the Welsh Mountain Pony have similar markings. There are also quite a few breeds where these types of markings are common, like the Arabian, yet SW1 is not believed to be present. That complicates the search for sources in breeds where a variety of white-producing mutations are found – which is actually the case in most breeds. Even the presence of blue eyes in a line may not indicate the presence of SW1 in breeds where it is known to be, because some blue-eyed horses have been testing negative for the (currently) known forms of splash white.
With luck those other blue-eyed horses will prove to have a newer mutation. That is the case with the other four formally identified forms of splashed white. The founder of the most common of those, SW2, is a known individual. While she was not named outright in the original paper, the information given matched that of the 1987 Quarter Horse mare, Katie Gun, dam of the famed reining horse, Gunner. The suspected founders of the other three were all born in the last two decades, which would suggest that mutations of this type are more common than originally thought.
And this is probably a good place to jump over to the subject of my friend’s albino dog, since that involves recessive genes, separate mutations producing similar colors, and the search for founders. I’ll start that topic in the next day or two.