For Artists


In the previous post, I talked about the two things that cause horses to have small dark spots on a white background. The first was the leopard pattern (Leopard Complex + Pattern1) and the second was the homozygous tobiano pattern. In this post, I want to talk about how dark spots on a white background are different in dogs.

Dalmatian dogs look like leopard appaloosas. It’s the same white background and the same small, round spots of color.  But Dalmatians are genetically very different from leopards. In fact, they have a lot more in common with the homozygous tobianos. That’s because they are “pinto” dogs. They just happen to be missing (or at least mostly missing) their dark patches. In fact, if you can imagine someone starting out with a classic tobiano horse – dark head, large round areas of color on the body – you have a good idea of what the basic piebald pattern is in dogs. In fact, in some countries the name for tobiano and the name for this pattern in dogs is the same: plating. Plattenscheck, platenbont – plate pinto. It makes sense, since tobianos have large “plates” of color on a white background. These dogs do, too. Or at least they started out that way. Here is a popular sire of English Setters from a little over a century ago.

His pattern is very reminiscent of tobiano. But breeders did not care for the patches, so they began breeding away from them.

In dogs, this kind of pattern is often called “extreme piebald”. It is still a “pinto” dog, but it doesn’t have a lot of color left, even on the face. English Setter breeders were not alone in this preference. The Dalmatian breeders were selecting for the same thing. They did not want patches, or even dark ears. They wanted all-over round spots.

Those round spots, which are visible in all three of these English Setters, look a lot like cat tracks to someone familiar with tobiano. What makes them different is that they aren’t actually part of the plating pattern. They are a separate thing entirely. For English Setters and some of the other sporting breeds, that’s the “Belton” pattern. The more technical names for it – ticking and roaning – are unfortunately for us horse people, already taken by very different patterns. So for now we’ll just use Belton to avoid making this any more confusing.

Belton adds dark spots of color to the areas the piebald pattern leaves white. What dog breeders have done is manipulate the scale and spacing of those spots of color. All three dogs at the top of this post have what are believed to be variations on this kind of patterning. The English Setter to the left is of course the original Belton pattern. The Dalmatian in the middle is likewise has a Belton-type pattern, but he also has some kind of modifier that has made the spots larger, rounder and more distinct. (Some of the distinctive nature of his spots are, of course, because he is a sleek-coated dog compared to the setter.)  The Australian Cattle Dog at the end has a Belton-type pattern that was modified to the other end of the spectrum, with spots that have gotten smaller, less round and less distinct. In some breeds, this is what is called Roan. There is some debate about whether Roan and Ticking in dogs are truly separate, or just variations on the same gene. I am not aware of any papers yet published with molecular studies, but it does seem that roan dogs, when outcrossed to non-roan breeds, end up with offspring that look a lot like the Belton setters. Certainly whether these are separate, similar genes or the same gene with layers of modifiers, the end result is that dogs have independent factors that will “recolor” the area that a piebald gene left white.

It didn’t seem that horses had that, at least not until recently.

In 2009 a French sport horse, Vision Morinda was foaled.

Clicking on the image above will take you to the website for her breeder, and her page which has many high-quality photos of her at all ages.

At first glance, it is tempting to assume that Vision Morinda is a tobiano with very loud cat tracking. The problem is that she cannot be homozygous. Her dam is brown. (Note that the mare she is pictured with is a surrogate. Her dam, Scarlett Fontanel, is pictured here.) But perhaps even more intriguing is the fact that her spotting seems to have intensified as she matured. That’s something that is typical of the Belton patterns. As most people are aware thanks to the Disney movie, Dalmatian puppies are born white and develop their spots later. That’s true of the English Setters and the Australian Cattle Dogs. Here is my friend Mary’s (extremely cute) Cattle Dog mix, Volt, as a puppy. (Thank you, Mary, for letting me share your photos!)

As you can see, he looks like a white dog with black patches. He is an extreme piebald. That’s why he has white ears. Well, mostly white ears. He was already starting to show some spotting there. His back and sides, however, looked white. But here is Volt today, as a grown dog.

As you can see, he developed his ticking – the Belton-type pattern – over time.

In a less dramatic fashion, Vision Morinda seems to have spotting that intensified as she matured. (Her breeders even comment on her page about the surprise of getting an English Setter color on their horse.) The spotting on her is also different, visually, from a typical tobiano with cat tracks. The pattern is evenly distributed. The spacing does change somewhat (notably across her shoulder) but it still is pretty consistent across the white areas, rather than clustering into spots or patches. It looks like the ticking you would see on a dog, not a horse.

This raises the question of whether there is some factor in horses that can add ticking – a Belton pattern, so to speak. I have a few more horses to share, all with odd spotting patterns. None are quite like Vision, but all have unexplained dark spots inside white patterns or markings. They all come from my “weird stuff” files. That’s where I put things that don’t make sense, or just seem “off” in some fashion. Sometimes enough of them accumulate – like the odd late greys from a few months ago – that it seems like there might be some thread connecting them all. I am not sure these horses really have a common thread, because they do have some visual differences, but I’m going to start posting them just to see if more turn up. That’s what happened with those greys (I have more that I need to post in the future, by the way!) so maybe sharing them will bring others out of the woodwork!

(Images at the top of the post are courtesy of Wikipedia. Images of historical English Setters come from The Pointer and Setter in America, published in 1911, and Country Life, Volume 22, 1907.)

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Images of leopard appaloosas with Dalmatian dogs are always eye-catching. Certainly they can look quite closely matched, like this Polish Malopolski and his buddy. Even so, the patterns in the two species are very different in terms of what is really happening to the pigment on the animal. That’s probably off in the weeds for most owners and breeders, but for artists the distinction is actually pretty important.

This touches on one of the reasons why artists who develop an interest in horse color often have such a different perspective. Usually the kind of information a breeder needs is predictive. That is, they need to know what might likely result from crossing this to that, or what they might need to cross if this particular end result is what was wanted. What artists need to know isn’t about prediction nearly so much as it is about possibilities. Not so much what might happen, but what could happen – even far-out-there, not-very-likely, could happen. That’s because artists often want to add something for interest or for composition. For those producing realistic art, that has to be done within the constraints of what is possible. It doesn’t necessarily have to be likely, but it does have to be possible. This unique perspective became apparent to me a number of years ago when I gave my first presentation on horse color. In the question and answer period afterwards, someone in the audience asked if a horse could be both dappled and fleabitten at the same time. It was clear that was not the sort of question my fellow presenter, Dr. Sponenberg, often heard. But it is precisely the kind of question that equine artists ask all the time. Scientists might not notice this kind of detail on an individual horse, but for someone who paints horses, this kind of information – does this happen with this? – has a lot of practical value.

So why do artists need to understand the process behind appaloosa patterns? Spotting is a useful tool, because it breaks up positive and negative space. It makes the horse more visually interesting. If you are particularly clever, it can be used to draw the eye in a way that works with the composition, or to hide flaws. But spotting doesn’t just happen anywhere. It follows rules, and those rules depend with what is happening with the pigment. Understanding the underlying mechanism makes it far less likely that you’ll add some interesting detail that isn’t realistic. When dealing with rare combinations of colors and patterns, it might be difficult to find a reference image to consult. Knowing the process can tell you if there is a reason to bother looking in the first place, because it tells you what is possible. (And when you wing it without a reference, the knowledge will make for more reliable guesses.)

“Trouble”, sculpted by Sarah Minkiewicz-Breunig and glazed by Lesli Kathman.
In the collection of Melissa Gaulding.

This is a ceramic collectible with the kind of spotting (often called cat tracking) seen in homozygous tobianos. It’s a really popular effect. In my normal job (the one I have when I am not trying to get a horse color book to press), I have produced quite a number of these. The problem comes when this gets confused with leopard spotting, and most especially what happens when leopard patterns are combined with the tobiano pattern. That brings us back to the image at the beginning of the post. These three images – the leopard, the Dalmatian, and my ceramic foal –  represent three very different scenarios in terms of the underlying process. I want to take each, one at a time, and explain how they are different despite looking so similar.

This is the typical nose-to-toes kind of leopard. Most people would think of this as a white horse with black spots that have been superimposed on top. That’s not really accurate. From a genetic standpoint, this kind of horse is a two-step process. First she has inherited a gene that progressively adds white hairs to the coat. Those hairs, over time, are going to produce the fairly distinctive pattern known as varnish roan. If the pony in my illustration just had that first gene, she would look like a black version of this pony.

That first gene, known as Leopard Complex, sets things up for leopard but it doesn’t make leopard patterns itself.

That happens when the horse inherits a separate patterning gene in addition to Leopard Complex. In this case, that patterning gene is called Pattern1. What Pattern1 does is take the white from Leopard Complex and amplifies and organizes it. So while our horse looks like she is white with spots, it is perhaps more helpful to think of her as a horse that was roan, but Pattern1 has now taken that mixture of white and dark hair  and reorganized it. Underneath the white hair, what that horse may look like is closer to this.

This is what the underlying skin looks like. She probably does have some truly white skin in the area where a blanket pattern would go. Pattern1 does amplify the white, after all. But under it all she isn’t really a white horse, at least not in the sense that most people would think of as true white. She is more like a roan horse that has been modified a bit. That’s why even nose-to-toes leopards have faces that are shaded much more like a grey than a cremello, because for the most part the face has dark skin, not pink skin. And that is why a pintaloosa looks like this:

The true white areas of the tobiano pattern cover over the appaloosa pattern. The spots from the leopard pattern don’t spread over onto the tobiano pattern because the process with Pattern1 isn’t “add dark spots to the white”, it is “organize the roan into spots.” So the spots don’t happen where the tobiano pattern already took all the roan away. Without the color there in the first place, Pattern1 has nothing to work with.

Of course, if we moved our tobiano pattern out a bit, encompassing more of the dark skin and butting it up close to the “blanket” skin, we could probably get something that looked a bit like the leopard spots migrated over some of the tobiano.

Even so, the spotting is still concentrated in such a way that shows it is an appaloosa pattern with a tobiano pattern layered over the top of it. The spots on the flanks might look like they are in the tobiano white, but really they are just in an area that was already white from the action of the Pattern1 gene. The action is still the same. The tobiano is there adding true, pink-skinned white on the horse, and underneath it Leopard Complex and Pattern1 are just doing their thing.

Even with the tobiano bumping up to the pink-skinned areas of the leopard pattern, it still looks different from the kind of spotting that comes from a horse having two copies of the tobiano gene.

This is a (presumably) homozygous tobiano with cat tracks. Whereas Leopard Complex is a roaning process that Pattern1 takes and organizes into the leopard pattern, this type of spotting is more like a not-entirely-successful attempt to add some more color to a horse that already has large patches of color. Unlike the existing spots, which are large and opaque, these new spots are small and vary in opacity. Some just come through in specks.

Cat tracking tends to cluster around the existing spots to some extent, almost as if these new spots want to occupy the same general area as the existing spots. This is quite different from the spotting on a leopard, which tends to be dispersed across the body.

The exception is the hooves. Tobianos with cat tracks often have a concentration of spots around the coronary band, often turning the hoof completely dark or nearly so.

There are spots on the legs, but typically they are not as numerous as the ones around the feet. The same is true for the face. This is the face that goes with these feet. He does have a few spots in his blaze, but they are not extensive.

So how is this different from the Dalmatian? Well he really is a white animal with colored spots added on top. In dogs, the gene for this is usually called Ticking, but since ticking means something different in horses, I am going to use the older English term for the pattern, which is belton. This post has run really long, so I’ll split that over into a second part. And why delve into the belton pattern in dogs? Because lately there has been a handful of horses that have turned up that just might have that kind of spotting. At the very least there are horses with dark spots inside their white markings that are not tobiano cat tracking and not leopard patterning. More on those will appear in the next post!

It has been exciting to see that the recent paper on horse color and cave art has gotten a lot of attention in the mainstream press. It is great to see scientists like Rebecca Bellone, the lead researcher from The Appaloosa Project, recognized for their work. I also love the idea that an area of study traditionally connected with agricultural and veterinary science could be used to better understand seemingly unrelated fields of archeology and art history. It makes sense that in understanding the horse, whose history is so intertwined with our own, we gain insight into ourselves.

That is the larger picture. From the smaller picture that is the focus of this blog, the study offers some big surprises.

To adequately explain, I’ll need to expand on the comments that were made in the earlier post on gene locations. In 2009, the paper “Coat color variation at the beginning of horse domestication” was published. In that study, ancient remains were tested for the presence of color mutations. The range of tests available at the time included:
Extension (black/red)
Agouti (bay/black)
Cream
Silver
Frame
Sabino1
Tobiano

Those tests determined that all but the frame gene were present among the early domesticated horses. That is certainly in keeping with the theory that frame is a New World mutation. It also showed that in the wild populations – horses living somewhere between 15,000 and 3,100 BC and predating domestication – the only mutation was black. Black horses were found among the wild populations in Romania, Ukraine and the Iberian Peninsula. The other populations, which included remains from Siberia and Germany, were entirely bay.

The two patterning genes, Tobiano and Sabino1, were found in remains of domesticated horses. That is in keeping with the idea that spotting mutations are linked to selection for tameness. The Russian Farm Fox study is often cited as a good example of this, but most people familiar with newly introduced “pocket pet” species have seen this in action. It usually doesn’t take long after a species becomes popularized before spotting patterns begin to appear.

What makes the cave painting study so fascinating is that the appaloosa patterning gene was found in a wild population. And it wasn’t just one horse. Of the thirty-one samples, six were carrying the mutation for leopard complex (Lp). Were someone to assemble a random sampling of modern domestic horses, it would be unusual to say the least to find that kind of ratio of appaloosas to non-appaloosas.

Also interesting is the fact that while there were six leopard complex horses, there were no chestnuts. Chestnut is found in the Przewalski Horses, where it has been documented as far back as the early twentieth century in skins taken in Mongolia. In the cave art study, there was a single Romanian sample that tested as carrying chestnut, so the mutation did exist at least in that population.  It would seem to be rare compared to leopard complex, and not nearly as old. The German samples with leopard complex date between 15,000 and 11,000 BC, whereas the Romanian with the chestnut allele is 4,300 BC. This is interesting when one considers how in many primitive European pony breeds, chestnut is non-existent, or when found is considered proof of foreign influence. It also gives a certain level of credibility to claims made by both Gypsy Cob and British Spotted Pony breeders that appaloosa coloring was once part of the native population.

It is also interesting that this mutation occurred in a wild population, and was obviously perpetuated, despite the fact that homozygous leopard complex horses have a defect. They are blind in low-light situations, which should act as a negative selection factor. None of the horses tested as homozygous for leopard complex.

Limitations

As exciting as the results of the study are, some limitations have to be remembered. Probably the most important is that this was a really small sample set. Getting usable genetic material from ancient remains is difficult, which is why there are only 31 samples. Broken down by time frame and geographic location, you end up with even smaller groups. These tests can certainly confirm that a mutation was present, but it is hard to draw any firm conclusions about the whole of the ancient horse population based on so few animals.

We also only have a partial picture, because we only have a partial set of color tests. The previous study, done in 2009, used some of those same samples. Without the leopard complex test, which was not yet developed then, we only knew that the wild horses were bay or black. With the new test, we now know that, yes, they were bay and black – and some where varnish roans (leopard complex). We don’t yet know if they had the patterning genes that turn leopard complex into true leopard patterns, though certainly the cave paintings would suggest that this was so. Likewise, we assume that the original horses were dun, since that coloration is associated with wild equines, including the last remaining wild horse. A completely reliable test for dun is not yet available, so that part of the picture is incomplete as well. Those bays and blacks, now known to in some cases be bay or black varnish roans, may later prove to be dun and grulla varnish roans – or not!

We know they were not silver or cream, since those can be and were tested. But as new color tests are developed, we may later learn that some of those horses were also roan or grey or splash. It may be that varnish roan will eventually lose its place, but for the moment it is the oldest tested pattern.

I have wanted to bring up a more technical aspect of horse color for a while, but have struggled with the best way to present the information. Part of the problem is that the way we talk about horse color is misleading. For this to make any sense, I will have to clarify some terms.

We often talk about horse colors as if they are genes. We say, then, that a horse like the one pictured above has one copy of the “sabino gene” and one copy of the “tobiano gene”. It is true that the “torn tissue” look to his pattern is very typical of what a horse looks like when it has both Sabino1 and Tobiano. He is a Spotted Saddler, so he would likely test positive for each color. Saying he has the Sabino1 gene and the Tobiano gene is a simple way to get that idea across.

The trouble is that there is not a specific Sabino1 gene. There isn’t a Tobiano gene. Sabino1 and Tobiano are mutations of an existing gene. When we say that a horse has the “tobiano gene” or the “not-tobiano gene”, what we really mean is that the gene that was there from the start is either mutated (tobiano) or not mutated (non-tobiano). This makes sense when you think about it. Why would an organism carry around a gene that is essentially the absence of a trait?

This might seem like semantics, except that some of what we think of as separate colors occur on the same actual gene. They are different mutations, but they share a location. In the case of Sabino1, the mutation occurred on a gene known as KIT. Other mutations found on or very close to KIT are tobiano, true roan and dominant white. This might not seem important until you remember that an animal has two copies of any given gene, one from each parent. It can only give one to any individual offspring. If a horse only has two KIT genes, then it can only carry two mutations – one on each copy of the gene. That means you only have two slots to fill with KIT mutations. A horse could be homozygous for tobiano, but then he could not also carry Sabino1. His two KIT slots are already filled.

This probably makes more sense when it is understood that most color mutations are one-time events that happened a very long time ago. Sabino1 has been documented in Siberia in the early Bronze Age, so it is at least that old. Horses like the one pictured here descend in an unbroken line from whatever early ancestor carried that first Sabino1 mutation. One of his KIT genes is that same gene with that same mutation. His other KIT gene comes from the whatever horse carried the first tobiano mutation. That pattern has been found in Eastern Europe later in the  Bronze Age, so like Sabino1 it is really old. Were he not a gelding, he could in turn pass on one of those – either tobiano or sabino1 – to his offspring. One, but not both.

This has implications for artists like myself because we tend to mix-and-match the details of different patterns to get certain visual effects. What we have to be careful about is whether or not the limitations of gene locations make something impossible. If a horse can only carry two KIT mutations, and true roan and tobiano prove to be on KIT or linked to KIT, then is a homozygous tobiano roan possible? Is a roan tobiano with cat track markings – a trait closely associated with homozygosity in tobianos – accurate? And what about the other colors and patterns that have not been mapped to a specific location? What conflicts will become apparent when more mutations have known locations? We know, for instance, that the leopard complex gene (varnish roan) is not located on KIT, but what about the patterning genes that work with leopard complex to make the more vivid appaloosa patterns? It is often assumed that all combinations are possible, though they might be so rare that actual living animals cannot be found with them. That is probably a mistaken assumption, with some combinations not possible because of location conflicts.

This also has implications for people who study horse color. Homozygous tobianos are an interesting example because they obviously have two KIT-related mutations. Still a high percentage of homozygous tobianos have face markings. The commonly accepted wisdom is that tobiano by itself will not place white on the face, yet KIT is often assumed to be involved in ordinary face markings as well as the sabino patterns. Does the fact that many homozygous tobianos have broad blazes suggest that some sabino patterns are not, in fact, located on KIT? Or does it suggest that in its homozygous state, tobiano does start to place white on the face?

It is also important to breeders, who may find that attractive combinations do not necessarily breed true. Many Paint Horse breeders have already noted this situation with roan tobianos. Roan has not yet been definitively mapped, and it is thought to be close to KIT rather than on KIT. Still genes that sit close to one another tend to travel as a package, and that is definitely the case with roan and KIT. Roan tobianos typically have a roan parent and a tobiano parent, and they usually pass along either roan or tobiano to their foals, but not both.

Gene location is pretty technical stuff, but the information has a lot of practical uses.

As many people have noted, the term “sabino” has become a bit of a catch-all for a lot of visually different patterns. In this way it is a little like “overo” was ten or fifteen years ago. At the time, the term overo was used to mean “not tobiano”. As the different kinds of overo have become more widely understood, many have dropped overo in favor of more specific terms.  But when something doesn’t quite fit tobiano, frame or splash, it usually gets classified – for the moment at least – as some kind of sabino.

In the upcoming book, I attempted to separate out some of the different forms the pattern we call sabino takes. Because only one form of sabino, Sabino1, can be tested at the moment, we don’t actually know if the patterns that are visually different are in fact genetically different. (We already know some things that look virtually the same can be genetically different!)  But it is true that some types of sabino can be found in some breeding groups and not others. It’s also true that some of these variations don’t fit the stereotypical “rules” often assigned to sabino. In fact, quite a number of them are likely to be misidentified as something else.

The pony mare in the picture above is a good example. Many people use high stockings and little or no face white as a clue that the horse or pony has a minimal version of the tobiano gene. (Although it isn’t the best picture, if you look you can see she had some white hairs on her forehead but no other white on the face.)  She’s not a tobiano, though. She’s a Hackney pony, which has not had tobiano in the gene pool since the early 20th century.

The one back leg does give a bit of a clue, since the white goes up the front of the leg rather than the side. This overlay illustration of a tobiano and a typical sabino pattern shows how the difference in the placement of white on the leg typical for each pattern.

That is often a good indicator, though it always has to be remembered that “typical for the pattern” is not necessarily the same thing as “always must be so.” The fact that tobiano is not part of the gene pool is a much more reliable indicator. What’s more, this kind of sabino pattern is not really uncommon in Hackneys. In the book I called these Unbalanced Sabinos, because they break the general rule that flashy white on the legs is usually matched with flashy white on the face. As these types of sabinos go, this little mare is actually pretty minimal. There are Unbalanced Sabinos that have extensive body white and very little white on the face.

Unbalanced Sabinos also break the rule posed by some writers that the sabinos have white on the chin or lips. This was my old Walking Horse gelding, Master.

He had a star and a snip, but no white on his lips or chin. Not only was it unusual to have four white legs without much face white, his leg markings were themselves unusual. The angle on this photo does not show it well, but there was a dramatic difference in the height of his front stockings, which rose in the front to his knees, compared to his hind socks. That was actually what caught my eye when I first saw him, because it is unusual for the front legs to have more white than the hind ones. He also had a belly spot half way between his girth and his sheath.

(And no, he was not a poster child for classic conformational ideals.)

One of the reason sabino variations have been on my mind was this excellent blog post by my friend Sarah Minkiewicz-Breunig. In the post, Sarah talks about the value of taking reference pictures for sculpting. Like Sarah, I am a huge believer in amassing a huge collection of reference pictures. There really isn’t any substitute for looking at hundreds and hundreds of variations of the same pattern. But even more than that, I would recommend the practice of sorting that collection. Nothing helps the eye spot trends like arranging like with like. That was how the different visual categories of sabinos were developed for the book. Stacks of sabinos were sorted into groups that were visually similar. In some cases, I pulled patterns off one body type and transferred it to another. You’d be surprised how often breed type can override your eye when it comes to spotting similarities (or differences) in patterns. Transferring the pattern over to a different body type can force you to really see things. That’s one reason why the illustrations in the book are on generic horse shapes rather than ones specific to the breed or type being discussed.

I had a few more detail shots of Colt, my friend Marge’s elderly fewspot gelding who was used in yesterday’s post.

As I mentioned in an earlier post about mottling, homozygous appaloosas like Colt often have more pronounced face mottling. Here are some pictures of his muzzle.

In my experience, homozygous appaloosas seem more likely to have this kind of mottling, where it looks like areas of pink skin with an overlay of small, dark spots.

They also seem more likely to have mottling around the eyes. (Although it is not something that changes the look of the eyes, homozygous appaloosas are also night blind.)

Here is the muzzle of the snowcap appaloosa from this previous post. (His nose is a little dirt from wuffling the ground, so his nose doesn’t look as pink.)

He has less pronounced mottling around his eyes, but he does have it.

Here is another body shot of him. Notice how light his front hooves are, even though those legs are solid (and black-pigmented).  Also note how very white his hindquarters are. That is one way to know he is not a false snowcap, because the real ones often have underlying pink skin that give them that really, really white look.

If you look closely at the lower legs on this fellow, you can also see that he has the bronzing effect that someone mentioned in the comments section of yesterday’s post. He is a bay horse. See how red the upper part of that leg looks, and the difference in tone at the knee? But when you get down to the hoof, the ankles are a silvery buff. That’s one of the other things that the leopard complex gene can do, though it doesn’t seem to do it all the time. I hope to make a longer post about it in the future, but I’d like to gather more photos for it if I can. (If you have photos of appaloosas that you have taken that show an oddy, hard-to-categorize base color, that you don’t mind appearing on the blog, feel free to send them. Just click on the sabino illustration to the right, and it will give you the contact information.)

Before I do that, though, I have a puzzler of an appaloosa that I will post tomorrow.

Another Layer of Complexity

So appaloosa patterns depend on a “master switch”, which, by itself, produces a pattern most equine artists would know as varnish roan. It is also
responsible hoof striping, white sclera and mottled skin. When that master switch is paired with additional patterning genes, varnish roan is changed to the louder blanket and leopard patterns.

There is another factor besides the pattern genes that can change the appearance of a leopard complex horse. That’s because the leopard complex
gene is incompletely dominant.

Most horsemen are familiar with incomplete dominance because of the cream gene. A chestnut horse that inherits one cream gene will be a
palomino, while if that same horse inherited two he would be a cremello. Leopard complex works much the same way; horses that inherit two copies of the gene will look different from horses with one.

The most basic difference is seen in the spotting. Horses with one copy of leopard complex are spotted. Horses with spotted blankets and leopards
are all carrying one copy of the leopard complex gene. Horses with two copies of the gene are (mostly) unspotted. These are the snowcap and
fewspot horses.

So a single varnish roan gene (Lp), when paired with the leopard pattern (PATN1) might look something like this:

While that same pattern gene (PATN1) with two copies of varnish roan might look like this:

And horse with the blanket pattern (PATN2) and one copy of the varnish gene (Lp) might look like this:

And that same gene (PATN2) and two copies of the varnish gene, might look like this:

There are other differences, too. Probably the most important of these to an artist is that while the hooves on the dark legs of a heterozygous appaloosa are striped, the hooves on the unmarked legs of a homozygous appaloosa will be predominantly shell colored. Remember the varnish roan from a few days ago?

His pale hooves suggest he’s probably homozygous for Leopard Complex. He doesn’t have a pattern gene, so there are no spots to remove, but his hooves are a clue.

Here is an elderly fewspot leopard with the same kind of coloring on his hooves.

They aren’t completely without stripes. Look at the difference on the varnish gelding’s marked foot, which is truly shell-colored, and the stripes on the dark feet. (This is easier to see in his picture than in the one of the fewspot.)

Appaloosa legs with regular white markings like socks and stockings will have ordinary shell hooves no matter whether the horse has one copy or two. Of course, marked feet on non-appaloosas vary in terms of how uniformly pale they are. But in general the homozygous appaloosa hooves look a little more striped than the typical marked foot, and a lot less striped (and a lot less pigmented) than heterozygous appaloosa hooves.

Here are the hooves on the fewspot:

Here is the hoof on a heterozygous (ie., spotted) appaloosa. Note that the legs in both pictures are dark, and in fact are even the same basic color. Both are genetically black horses that have the bronzing effect found in some appaloosas.

Here is the hoof of the same horse as pictured above, only on a leg with a white marking.

When horses have one of the major patterns like leopard or blanket, then the presence or absence of spots makes it pretty easy to tell whether the horse has one or two copies of leopard complex. It’s a bit harder with horses that don’t have an obvious pattern gene. Many varnish roans do not have spots, especially if the varnish pattern is very subdued. The hooves are often the best clue, though those are often hidden in pictures. Hoof coloring can also be hard to determine in pasture-kept horses. The hooves in this post are all on pasture horses that haven’t been recently trimmed, so what striping is there is a little more muted.

Here is the hoof from the post about the pony Thumper, showing the stripes on a recent trim.

A word of caution, though. There are things that can make a horse look like a fewspot or a snowcap, besides the presence of two Leopard Complex genes. When paired with the appaloosa patterns, sabino tends to whiten the pattern and reduce the size of the spots, which can give horses the appearance of being homozygous. These horses are sometimes called false snowcaps or false fewspots. When looking at something that might be a snowcap or fewspot, check for face and leg markings. If the horse has flashy markings, his spotless appearance might be due to that rather than having two appaloosa genes.

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