Eye color


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The blog here continues to be somewhat silent while I work on the next book, “Equine Tapestry – An Introduction to Colors and Patterns“. What began as a reissue of the front portion of Volume I, Draft and Coaching Breedsface in color has (predictably) taken on a life of its own. The original text touched on the as-yet-unidentified pinto patterns, with an attempt to classify the different categories of sabino-like patterns visually. Since that time, quite a few more pieces of the puzzle have fallen into place, and that has lead me to do a major overhaul on that material.

One of the things that became clear to me with this new information was that the way I personally organize my files was leading to blind spots in my understanding. I have mentioned before that a huge part of my research involves massive notebooks with images and pedigrees. Because I am a visual learner, sorting things this way helps me make connections that I might otherwise miss.

Notebooks

I have organized information in notebook pages like these for more than 20 years. Soon after I began, I started sorting the information by breed. Because so much of my interest centered around which colors were present in which breeding population, this made sense. What I began to suspect, working on the new book, was that I needed to rearrange some of my notes by color groups, rather than by breed. The previous structure was great for seeing how some of the louder sabino patterning arose in the Arabian breed. Seeing how that worked convinced me that the louder horses were some kind of new mutation, and not just a more extensive expression of the existing “flashy white” in some lines. Laid out in a breed-centered notebook, it was clear how these louder horses – horses like Rhocky Rhoad – might come from flashy families (like Khemosabi), but their (numerous) relatives did not generally look unusual, while their own descendants most certainly did.

But this same structure made it harder to make connections about the colors themselves. The sheer volume of information – I have thousands of horses on file, and many times that number waiting to be included – made those connections more dependent on my working memory. Writing more has meant less time for musing, and with it the chance that I would make those mental jumps. When recent papers made it clear that my hunch about horses like Rhocky Rhoad were correct, I decide it was time to set up a parallel set of notebooks for the pinto pattern categories, starting with the W-series (W1-W20). I was hoping this would give me better insight into how the patterns within that group – the group previously called “dominant white” – worked. With luck, I might stumble upon the best way to present this very varied, and not-entirely-helpfully-nameed group in the new book.

I now have all twenty of the known W mutations, along with images of every known or suspected carrier, in a single notebook. The first thing that jumped out at me was something that has been a bit of a hobby horse for me for some time now. That was how many of these lines involved blue eyes. Of the twenty families, six have blue-eyed individuals. In some cases, like the W5 family member Sato (above), just have a blue segment. Others have a full blue eye, or even two blue eyes, thought that last is actually pretty rare.

This is not surprising to anyone who has looked at historical records of white-born horses. Blue eyes are not infrequently mentioned. They are mentioned in connection with some of the old European studs that previously bred white-born horses. Early researchers also comment on their occasional presence. Nowadays, a search on the internet will turn up any number of commenters that will tell you that this “obviously” means the horses carry a splash pattern. You can even find those who will assert that no KIT mutation ever produces blue eyes in a mammal.

That was part of why I included the image of the panda German Shepherd a while back. She has a newly-identified KIT mutation, and she most certainly has blue eyes.

FrankieSM

Interestingly enough, most white patterning in dogs has proven to be caused by mutations to MITF – not KIT. In horses, MITF is the gene associated with splash patterning – and with blue eyes. For those familiar with dog coloring, the “extreme piebald” found in many sporting breeds, the “color-headed white” pattern in Collies and Shelties, and many forms of “Irish Spotting” have all been mapped to MITF. None of these patterns is associated with blue eyes in dogs. There is a MITF mutation in dogs – the one that produces white in Boxers – that produces blue eyes on rare occasions, to this is not an absolute, but generally speaking these MITF mutations are not associated with blue eyes. (For more information on the different MITF mutations in dogs, this a good site.)

The common theory in horses is that these W-series horses must have a splash mutation as well. And they may. Certainly there are far more mutations for white patterning than previous expected. I have long thought that the numbers of blue eyes on the dominant whites, particularly among the founder horses (ie., the horse that carried the initial mutation) were just too high for them all to happen to have a splash mutation as well. I did not have an exact number, though – just a sense that it was high. But the new sort gave me a number – six of twenty. That’s a lot, especially with breeds where there is no evidence of the presence of the one splash pattern (classic splash, SW1) known to remain cryptic in its heterozygous state. The other “new” splashes are dominant mutations, and a good bit more obvious in terms of phenotype.

What is interesting is that the one horse that is often asserted by online commenters to “surely be a splash” is the well-known Arabian stallion Khemosabi. This is based on the fact that he has multiple blue-eyed descendants. What became clear as I resorted these records was that yes, he does have a number of blue-eyed descendants. However, all those in my files are also members of the two W-series mutations that occurred in his line. One would expect, if Khemosabi carried a splash mutation (at least, as we currently understand the pattern), it would appear in more than two lines. He did, after all, sire over 1,250 foals. Finding it in two lines, which also just happen to be those that have formally identified white spotting mutations, seems to suggest that the blue eyes are part of the pattern and not some additional inherited trait.

There are caveats to this, of course. Blue eyes are notoriously underreported. When I began to suspect that the louder sabino expressions in Arabians were new mutations, I printed out the markings files for the families where they occurred. So in my files are the marking diagrams for all the first generation Khemosabi descendants. It is quite possible that there are horses in that group with blue eyes that were not part of the registration records. Blue eyes in Arabians are still considered a serious fault, so there is some incentive to overlook it when filing a description, especially for an eye that is not completely blue. (I am always looking for images and records of blue eyes in Arabians, if anyone has them, by the way!)  I cannot also be sure that some of the other lines – the fourteen that are not included as having blue eyes – might not also have blue. In many cases, eye color is not mentioned at all,  and there I have defaulted to the assumption that the eyes were dark. That is not the same as knowing the eyes are dark, though.

My next task is to assemble the even larger group of suspected dominant white horses into one notebook. When that task is complete, I should be able to do another post about the status of the blue eyes in that group as well.  Well, that and get a little closer to a finished book!

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I think I need to work on final book edits every spring, because it seems to guarantee that a paper will come out within that time period. Animal Genetics has a short communication out with three new KIT mutations and one new PAX3 in horses. There are also two papers out on KIT patterns in dogs, which is new. Before this, the piebald patterns in dogs had been mapped to MITF, which in horses is the other site for splash white. The picture above is the German Shepherd that carried the de novo mutation. (I must give a special thank you to her owner for allowing me to include it here.) I had intended to put together a longer post on this pattern, known as panda, because it touches on the subject of blue eyes in KIT mutations. She obviously has blue eyes, and her owner confirmed for me that some of her descendants have had a blue eye or blue segments in their eyes. This follows the pattern that I have seen in the historical records of some suspected Dominant White horses (also presumed to be KIT mutations). Blue eyes do seem more common in the originators, and then appear to occur sporadically – often in a less pronounced degree – in the descendants. Interestingly enough, the MITF mutations are not associated with blue eyes. In fact, this family of Shepherds was the first instance I noted where blue eyes in dogs were linked with a form of white spotting so I was particularly happy to see the mutation formally identified.

What is interesting about the new equine discoveries is that they really do not fit neatly into existing naming categories. The KIT mutations have been assigned numbers in the “W” series, but at least one appears to be subtle white-booster rather than a true dominant white. I had been urged by a couple of researchers, as I got close to my publication date, to avoid the use of the term “sabino” and just use “white spotting”, and I see now why. I suspect this will become more complicated as time goes on and more mutations are identified. One thing does seem clear, and that is that several of these sites mutate often – apparently in ways both large and small!

Just as I did with the book last year, I’ll be updating the text to reflect this new information for the new full-color supplemental book. I had feared there might not be much new information, but this coupled with some of the things I have been researching in the last few months should make for a lot more content as well as more abundant (and colorful) images!

I wanted to get pictures of one of the new horses at our barn, Dutch, to use for a post on sooty patterns. Dutch was interesting because he has the very dark forehand that some sooty buckskins get. I also thought artists that read the blog might find the abrupt transition between his body color and the black front legs interesting.

I had only seen Dutch at a distance, but I had gotten the impression he had somewhat paler-than-usual eyes. Light brown eyes are not uncommon in buckskins or palominos, so that would not have been unexpected. When I got close enough to take this picture, the reflection from his eyes looked off. (All the images in this post are larger than they appear, and since the details are small, I highly recommend clicking them to see the larger version.) Instead of looking pale brown, his eyes looked like the reflective gleam was in the wrong place. That is more noticeable in this face shot.

Over the years I have learned that odd reflections in the eyes sometimes mean the horse has a blue segment, and sure enough, that was the case with Dutch. Although he has no white markings at all, both of his eyes have flecks of blue. The largest one is located close to the bottom of his right eye, and is what is giving the odd reflection.

As can be seen in that photo, he has a number of blue flecks in that eye. His iris also has irregular patches of golden brown and darker brown, giving the whole eye a marbled look. Although it was more visible in brighter light, even without the light directly hitting the eye the blue areas could be seen.

His left eye had smaller flecks of blue that were much harder to capture on film. (This is the image that would most benefit from clicking, since the flecks are so small.)

He would be an interesting horse to test for splash white. So far a couple of individuals without white markings of any kind have tested heterozygous classic splash white (SW1). Perhaps Dutch carries SW1, too. It is also possible that there is some other yet-unknown cause for the blue sections in his eyes.

 

Nicole Jory shared a photo of her appaloosa pony, Jack, in the comments section of the post on snowflake patterns. I wanted to share him here because he is also a great example of color shifting on a bay appaloosa. His stockings hide it on the other three legs, but if you look closely at the left foreleg you can see the odd pewter color where the leg would normally be black. For some reason color shifting seems more common on black appaloosas than on bays, so I was happy to find such a good example.

He also has what I call an “occluding spot” over what would probably have been a bald face. Nicole suspected he was carrying a splash pattern, and I would tend to agree. Blue eyes and this type of face marking are very common in Appaloosas that trace back to Bright Eyes Brother, who is believed to have carried classic splash (SW1).

Jack will make a good jumping off point for the next set of posts about those occluding spots, which I hope to post later over the weekend.

Anyone who has followed the results from the new splashed white tests knows there have been some really surprising results, both in how many horses test negative, and in some of the horses that have tested positive. For those of us that had been studying “classic splash” (splashed white-1) for a while, some of these were perhaps less surprising because we knew that there were blue-eyed horses that looked somewhat like splash, but that did not produce the classic pattern (what we believed to be homozygous). But even there, there have been unexpected surprises. Probably the most dramatic was the Bald Eagle family of Australian Paints. For those that have the Gower color book, this is the splashed white family that was profiled there. I would have guessed (wrongly!) that those were homozygous classic splashes (SW1/SW1) with some type of sabino patterning.

I may have another wrong guess. I have believed that classic splash (SW1) would be found in Marwaris and Kathiawaris. There are certainly horses that have the right kind of pattern. I had hoped that the test on the blue-eyed tovero Marwari above would come up positive, but she was negative. It would have been better if we could have tested one of the horses with the classic pattern like those linked, but it is not a breed with a lot of representatives in the West, so I was tickled to have any blue-eyed horse to sample.

This test coming up negative makes me wonder if those are homozygous splashed white-1 horses, or if there is another mutation that truly makes the same pattern. The Bald Eagle horses at least have some visual differences. I had a particular interest in seeing if the classic pattern (SW1) was in the Marwaris or Kathiawaris because they are so far removed from the breeds where classic splash was first documented. When Valto Klemola found and named the splashed white pattern (what would eventually be splashed white-1) in 1931, he believed it originated in the northern European breeds. It certainly is more prevalent in those breeds than anywhere else except perhaps the American breeds. Finding it in such a genetically distant breeds like the indigenous horses of India would be really interesting, since it would suggest this particular splash mutation is very old.

My friend’s blue-eyed mustang Jag also tested negative for all three splashed patterns and for frame. He has been pictured on the blog before, but here he is again.

It will be interesting to see how many of these horses have splash-type mutations (MITF or PAX3), or if they have unrelated mutations that also happen to give horses blue eyes.

 

It can be really hard to get good shots of horse eyes, so I was really pleased to get a number of good shots of this Pintaloosa mare and her partially blue eyes. The placement of the blue segments certainly give her an unusual expression. This first image shows how her left eye has a blue section towards the upper front of her eye. The apparent shape is accurate – none of the bluish area is glare – since it is consistent across a number of images.

Here is her right eye, with a blue section on the lower side. Notice how a thin line wraps up along the back edge, and how uneven and inconsistent the blue area is. (The blue coloring on the left eye was uniform.)

Here she is looking forward with her mismatched eyes, one with a blue bottom and one with a blue top.

Here are some full-body shots of her, showing her varnish roan (leopard complex) and tobiano patterns. The varnish mark on the top of her tear bone is particularly noticeable in the first picture, and the mark across the nasal bones in the second one.

 

In the previous post, defects in the eyes were used to help identify a homozygous merle. That is often a strong indicator, but there is one situation where that is not always helpful. Collies, and some of the closely related breeds, have a number of issues with their eyes that are unrelated to the merle gene. Compare the normal eyes of the merle Shetland Sheepdog, above, to the eyes on the merle Rough Collie below.

Like the Great Dane in the previous post, this dog has an eye that appears to be too small and set incorrectly. Her left eye, which is blue, also has a distorted pupil similar to the one seen on the Dane. It is more obvious when viewed from the front.

Although it might look like she is looking to the side in this shot, her pupil actually skewed over toward that corner, giving her a cross-eyed look.

She is not a double-merle. Her pattern is typical for a single merle with moderate white irish patterning. Whatever is wrong with her eyes, it is probably separate from her merle coloring. Her one blue eye makes the problem more noticeable, but chances are she would have had issues whatever color she happened to be.

And that is why distortions in the eyes on collie breeds are not necessarily proof that the dog is homozygous for merle. Fortunately for identification purposes, most double-merle Collies are quite dramatically white so they are unlikely to be mistaken for a heterozygous merle.

But dogs like this one also point to the reason why using double-merles in Collie breeding programs is a bad idea, even when someone else made the ethical compromises necessary to create the dog in the first place. Because two copies of the merle mutation damages the eyes, there is no way to know if a homozygous merle breeding animal had eye problems unrelated to the merle coloring. Dismissing eye problems with the assumption that the heterozygous offspring will not be affected could be a mistake, because there is no way to be sure that the homozygous parent has otherwise normal eyes.

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