Tag Archives | SW1

Searching for another founder

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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.

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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.

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Eri-Aaroni, a son of Murto and one of the most influential stallions in the Finnhorse breed

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.

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The updated Splash White Project page

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Fergies Kitty Hawk, a classic splash (SW1/SW1) Miniature Horse mare owned by Pacific Pintos

As I mentioned in yesterday’s post, the Splash White Project page has been updated. I am still in the process of adding more horses, but the page is up and working now. It utilizes the WordPress Portfolio feature, which probably requires a little explanation since it is not entirely intuitive, nor is it really designed to work as the kind of visual database that I had in mind.

If you click on the Splash White Project link on the main menu, that will take you to the master page. There you’ll see information on how to submit horses for the page, and a little bit about the purpose of the Project. Underneath that you’ll find a number of small white buttons with different pattern combinations. Below that are thumbnail images of the horses currently in the database. The default is set to “All”, but clicking on the other buttons will allow you to sort the images so that you just see one category – say, all the SW1 homozygous horses, or all the horses that have come up negative on the tests.

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Spooks Hired Gun, a Paint Horse stallion that carries both SW2 and frame overo

From the thumbnails, you can either click on the image, which will bring up the full-sized image in a lightbox, or you can click on the horse’s name. The name will take you to the individual horse’s page, which has links to the owner’s website and links to the pedigrees (and sometimes photos) of the parents. More details on the markings (particularly the eye color) and test results are included as well.

The Portfolio format allows someone to easy sift through the images to see the differences between the patterns and pattern combinations. I have tried to break down the categories as precisely as possible within the limitations of what is currently testable. The one exception are the homozygous SW1 horses, which for the moment are grouped together even when other patterns are present. One of the benefits of using this system for the page is that it is relatively easy to add new categories and shuffle the existing horses around as new tests become available. I anticipate that happening the future, especially as research continues on the mutations that boost or suppress white markings and patterns.

I would also encourage anyone who has tested their horse for one of the splash white patterns to submit their images and information to the database. Every horse is another bit of information about what the various patterns can look like. That is also true even when the horses have tested negative. If you would like your horse included, I can be reached using the contact link (the small envelope on the main menu bar) or by the blog’s Facebook page.

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Macchiato

Freiberger

As I posted briefly yesterday, the new paper on splashed white had a lot of surprising information, not the least of which was the horse pictured in yesterday’s post. A number of people wondered about his identity, and most particularly about his breed. His name is Apache du Peupe, and he is a four year-old Freiberger. The Freiberger is also called the Franches-Montagne, which sometimes leads to confusion. The horses in the picture above (courtesy of Wikimedia Commons) are quite typical examples. Freibergers are among the last of the European light draft breeds, though in more recent years many breeders have focused on a slightly lighter riding type, which is why I choose to shift them – and a few others, like the Frederiksborg – to a later volume rather than include it in the draft and coaching breeds.

Because they were originally included in the upcoming volume, I had looked into the range of colors in the breed. Apache came to my attention during that time. Freibergers were already interesting because they had a well-documented family of dominant whites. Those trace back to a white mare, Cigale, born in 1957. She was the source of what eventually became the first formally identified dominant white mutation. Hers is the mutation that got the designation W1. That is what I thought Apache was, until I realized that he was not related to Cigale. In fact, his parents did not look all that different in color from the two horses pictured above.

Here he is again, from yesterday’s post:

Druck

This is his sire, Noble Coeur. This is his dam, Muscade. Both are clear bays with socks and minimal face markings. Apache and his parents are the kind of horses that sat in my “don’t fit the theory” file when I first wrote about maximum sabinos (sabino whites) in the 1990s. The horses that did fit that theory turned out to be Sabino1, the spotting pattern that results in a white horse when homozygous. All the horses that fit the theory had parents with a high number on my ranking scale for white markings, while most of the horses in the “don’t fit” file had parents that fell short. Typically they did have some white, but it was a stretch to say they were marked like the others. Had Apache and his parents come along at that time, they would have ended up in that same file. Many of the horses there (R Khasper, White Beauty, Puchilingui) were later identified as dominant whites.

So I wondered if Apache was another new dominant white mutation. But there was another aspect to him that made me wonder, and that is why – up until yesterday when he appeared in the splashed white paper – he was in my “mystery” files. If you look closely at his picture, he looks diluted. If he were a Paint horse, or almost any other American stock or gaited breed, I would assume he was buckskin. Here are more pictures that give that impression.

Cantering (with is spin visible to show no dorsal stripe)
Conformation (quite current, shot in 2011)

That was what was so unusual about him. His parents are, as the links show, quite ordinary bays. And even allowing for the fact that he probably has a good portion of white hairs mixed in his coat, the tones give the impression that the actual hair is diluted. His owners called his unusual color “macchiato”, for the coffee drink, which suggested that he was cream-colored in person. Since his parents were not diluted, and since I had no evidence that cream (or any other dilution) was present in the Freiberger, I wondered about the accuracy of his pedigree. Pattern mutations do appear, but a pattern and a dilution all in one horse?

And now with the publication of the splashed white paper, we know that is exactly what he has: a mutation that is both a dilution and a white pattern. Researchers parent tested him using 13 markers, confirming that he really was the offspring of the parents of record. What’s more, they tested blood, hair roots and sperm to rule out mosaicism. Mosaics are animals that have two separate sets of cells with different genetic coding. Horses that are patched with black and chestnut, for example, are mosaics. Apache is, genetically speaking, all one horse with the same genetic makeup throughout his body. They also looked at the genes currently known to produce dilutions, and found nothing out of the ordinary. So he’s not a cream, a silver, champagne, pearl or dun. He is what is called a de novo mutation – something new.

The new thing that he has is a mutation at the same location as splashed white, which is the MITF gene. The color Apache’s breeders named Macchiato is a form of splashed white. Technically that makes four identified splashed white patterns, although researchers declined to name his SW4, perhaps in deference to what his breeders were already calling the color. So far the other MITF mutation for which we have numerous examples to study, SW1, does not seem to have the diluting component. The third, SW3, is said to be rare and none beyond the two horses pictured in the paper have come to light so far. Neither of those two horses appear diluted, but two is not a lot of data, especially when one is too white to really evaluate base color on anyway.

But what is interesting is that Apache’s mutation has a human equivalent. The human Tietz Syndrome is caused by a similar mutation. The Office of Rare Diseases Research describes Tietz Syndrome this way:

Tietz syndrome is a genetic condition characterized by profound hearing loss from birth, fair skin, and light-colored hair. This condition is caused by mutations in the MITF gene.

A second human MITF mutation causes Waardenburg Syndrome. Again from the Office of Rare Diseases Research:

Waardenburg syndrome is a group of genetic conditions that can cause hearing loss and changes in coloring (pigmentation) of the hair, skin, and eyes.

So a similar mutation in human beings causes pale hair, piebald patches (in the Waardenburg Syndrome) and pale eyes. It also causes deafness, which was also true for Apache, who tested to be deaf.

That raises the question of whether or not other as-yet-unidentified splashed white patterns might not have a dilution component like that seen in Apache. Certainly several of the horses from the Bald Eagle line have a very similar base color to Apache du Peupe. I had assumed that, being stock horses, the were getting their diluted color from the other parent. It would certainly be worth looking at the members of that family to confirm that those with diluted base colors actually had a diluted parent. That isn’t something that ever would have occurred to me to look for, because “dilution” and “white pattern” were completely separate categories of colors up until yesterday. As I said, it is an exciting time to study horse color, because there really is something new to learn all the time!

So that’s three of the four mutations. Someone probably noticed that one got skipped. That is SW2, and if Macchiato complicates how we categorize mutations, that one complicates how we are naming them. I’ll open that can of worms in the next post!

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