Horse Color Genetics: A Little More on Sabino

Here is the last post I did on overo, but since I have learned much more and would like to do seperate posts, going a little more indepth on each overo type.

Sabino is a part of the KIT gene, which are a set of genes that share the same locus. Roan, dominant white, and tobiano all fall in as some of the others. It is also an incomplete dominant gene, meaning that, whether in heterozygous or homozygous form, the pattern will express itself in different ways.

Sabino is also classified as an overo pattern. However, it has so many different forms that many people don't know how to describe it. The following horses are all sabino:

While the two horses in the middle have very similar markings, the top and bottom one aren't even comparable. That is how much variation there is in the mutation.

The first three horses were all heterozygotes; one dominant copy of the gene. The last one is what is called 'maximum sabino', and it is homozygous for sabino, or SB1. Along with dominant white, maximum sabino can sometimes be confused for albino, but in reality it is, just like dominant white, like a giant white spot that covers up the color underneath. They always have dark eyes, unless combined with other genes which might cause blue eyes.

In the most recent equine genetics book available, The Equine Tapestry, Lesli Kathman talks a little about SB1 and why it has the number on the end. Scientists are anticipating more sabino mutations that are yet undiscovered, but SB1 is the only one that is testable at the moment.

Within the heterozygous range, the pattern can vary immensely, from almost not there, to a fully fledged pinto pattern that can be mistaken as nothing else. Because of this, sabino is hard to breed for. Minimum and maximum form within the heterozygotes is not neccesarily transferred from parent to offspring. For example: a maximum heterozygote could produce a minimum heterozygote, and vice versa.

Note: the difference between maximum sabino heterozygotes and maximum sabino homozygotes is tremendous; the former usually represents itself in the loud pinto form, the latter in the all white form.

Many heterozygous sabinos have some kind of roaning, making the patches less defined than many of the other pinto genes. Some have even been mistaken as plain 'roan' (also sometimes called true roan). Any of the above horses have just the tiniest bit of roaned out bit, but be careful when identifying sabino's, as horses that actually carry both roan and sabino will probably be more defined than you would think.

Sabino can be identified easily in a more maximum form, by the irregular splotchy patches that look like the horse was randomly splattered with paint, and is usually accompanied by some kind of large face marking and stockings. Minimum forms can be easy to mistake, however, for minimum forms of other patterns such as frame or splash. Sadly, I have no rules as to how to differentiate the two, other than the tendency to 'behave' differently. Maximum heterozygous forms can be almost indistinguishable from several of the dominant white mutations, especially within Arabians. The two arabians below have good examples of what some may not recognize as a pinto pattern.

In breeds where pinto colors are not 'available', like Arabians and Clydesdales, sabino is very much a part of. It has been noted, however that Clydesdales do not carry SB1, but almost every single one has some form of sabino. The mutation may be specific to the breed, but that is yet unknown. Notice the large face markings, tall stockings, and belly spots, which all are indicators of some kind of white patterning gene.

If many breeds allow sabino, but not other pinto patterns, the question my mind keeps wandering back to is this: should sabino actually be considered a pinto gene? In most cases, most horsemen don't consider bald face markings, tall stockings, or even small belly spots to be anything of consequence. And homozygous sabinos can barely be called pinto at all.

I would say, in my own opinion, that minimum heterozygous sabinos are much more common than maximum heterozygous sabinos. Even if you look up pictures of the former, there are many more than, because the owners don't see them as anything in particular, aren't labeled as such.

What is the Difference Between Paint and Pinto?

Among horse owners and enthusiasts, there is quite a lot of confusion on the subject of whether a horse is a paint, or a pinto. What is the difference? Is there a difference?

There is, in fact, a slight difference. But just by looking at a horse, you won't be able to tell. Any owner of a paint or pinto horse will tell you, 'Paint is a breed, Pinto is a color'. This is true to some extent, but not always.

Technically, the Paint horse is a breed. The APHA (American Paint Horse Association), because it is an official registry, doesn't allow just any paint-colored horse. They must have one parent that was registered as such, and another parent that is an approved cross-breed.

Many registries do this to allow for different types, and new blood. For example: the POAC, which is not a very old breed, allows for any POA that is crossed with an Arabian, Thoroughbred, Appaloosa, Connemara, among others, to be fully registered as long as they meet other height and color requirements. Through out-crossing, many different kinds of conformation are allowed for, whereas, if only POA blood were allowed, they would be mostly similar in build, in either a more Western type, or English type. In old breeds, like Arabians and Thoroughbreds where no outcrossing is allowed for purebreds, there is a much more typical type between all of them as a whole.

Even though it may seem that the Paint Horse is a color-oriented registry, any horse that is born solid either from two registered APHA horses or from one APHA parent and one approved outcross breed (the only out-cross breeds allowed are Quarter horses, Thoroughbreds, or Appendix (meaning 1/2 Quarter horse, 1/2 Thoroughbred)) can be registered as breeding stock. It is not the same thing as full-registry in that there are some showing restrictions, but they can produce very valuable or colorful foals by breeding back to another registered Paint horse. The horse below is a 'solid' paint.

A lot of people get confused when the owner of the horse tries to explain that their ordinary-looking horse is a registered Paint (breeding stock), but that is because most people who don't own horses don't know how registries, or genetics, work. The fact that two loudly-marked horses can produce a solid foal makes no sense. But in the genetic sense, it does. Another solid paint mare, below:

It is quite unfair, though; by reading through the APHA rules, I learned that irregular markings, or blue eyes, which both indicate some interesting genes that can produce colored foals, aren't allowed full registration.

Back to the other subject: what, then, is a pinto?

A pinto is defined by the fact that it is, and isn't, a breed.

Any horse that has paint-markings can be called a pinto. They may or may not be actually a different breed. For example: Tenessee Walking horses can be purebred, and also pinto color. If you don't know and you call them a pinto, that is totally okay, but the owner may sharply reprimand you and tell you that,  it is in fact a Tenessee Walker. Below is a paint-color Tennessee Walking horse.

Technically, there is actually a pinto registry. It's pretty cool; they are much more forgiving of breed, and you can basically double-register if you want. There are slightly more rules for registering stallions, but almost any horse that has paint markings, even with unknown parentage, can be registered. The mare below is double-registered as Half-Arabian, and also Pinto.

 In fact, any horse that shows two pinto characteristics but is not loudly marked can be registered as well. Which as basically taking into account some genetics. Registering a horse with the PtHA (Pinto Horse Association) can greatly increase a horses value, and all because of the color!

There are many un-registered paint-marked horses. Which, in any case, would be a pinto. I've found that owners of any Paint or pinto horse is very particular about calling them one or the other.

The final question: does it actually matter what you call them? To me, not really. When speaking in terms of genetics, I'll use either, although if I wanted to be technical I would use pinto because I'm only talking about the color, and not the breed.

It is fascinating how many registries there are. If you have a horse with absolutely no papers at all, there is very likely a chance you can register it somewhere.

Horse Color Genetics: Dominant White and It's Gazillion Mutations.....

Dominant white is basically a white spotting gene, similar to any of the pinto patterns. HOWEVER (and that is a big however), it is not as simple as all that.

Dominant white is not all that common, and it comes in so many different forms that it is hard to trace. There are 20 identified mutations, but only 3 you can test for. There are probably more since it almost seems like a progressive color, mutating just a little bit every time a horse is bred. That is why it is so hard to trace.

This particular spotting gene can come in all shapes and forms. The easiest to identify is almost all white; about as close to albino as you can get. HOWEVER, the eyes are dark, unlike cremello's and other double-cream horses. Think of dominant white as a huge white spot; whether it covers the whole body, or only parts, depends on the mutation. These can sometimes be mistaken with fully expressed sabino horses.

There is another way it can show up, too. It can also be more spotty, and even look sabino, or even any of the other pinto genes. On the genetics forum, sometimes people will post pictures of their unusual pinto horses that they tested for all the different genes they could test for, and still came back with recessive results. The verdict is that they must be some kind of untraceable dominant white gene. There is never any uniform pattern to partially spotted dominant white horses, unlike all the pinto patterned horses, which is also why it is hard for owners to identify.

The below horse is the founder of Dominant White 3, which is found in Arabians.

What's neat about dominant white is that it is present in quite a few all-solid breeds like Arabian and Thoroughbred, making quite a few look pinto-mix. But dominant white is accepted in those breed registries, wheras pinto is not.

It is thought, but not fact, that all of these dominant white mutations in homozygous form is embryonic lethal, resulting in what scientists think is an embryo which dies after a few weeks. This thought is based on the fact that all of the horses that have been tested for dominant white are heterozygous for the gene. Whether this is within each individual mutation or umbrella for all W genes is beyond me.

More information will be posted as soon as more information is available.  Below are all the traced mutations, but not all of the tests are available to the public yet. Check out W5!

Horse Color Genetics: Identifying Crop-Out Paints

Review: TO=tobiano, O=frame overo, SB1=sabino

One thing that confuses and frustrates a lot of non-geneticists is when they breed two paints together and the resulting baby is completely solid, no interesting pattern at all. But the one combination that totally doesn't make sense to a lot of people is when they breed two non-paints and the baby is paint. How do you explain this, and why does it happen?

As a side note, before I begin, I use paint and pinto interchangeably. In genetics, there is no difference, it is a patterned horse with pattern genes. Some people get into crazy arguements about which is correct, but there is no difference. If you are speaking about which is a breed, then generally Paint is a breed, whereas pinto is a color.

It's important to understand that pinto-patterned horses come in a lot of different varieties. Some are crazily patterned....

Some have only a minimal pattern, but are still obviously paint (well, the one below isn't super obvious, but you get the idea)....

And some don't look paint at all!

I know, you may be gasping, but I'm guessing both of the above horses carry some sort of paint gene. How do I know? And why aren't they as flashy as other paints?

Similar to other markings, all various genes are inherited from the parents. Paints don't just happen, they had to get them from somewhere. 

The horses above are what you might call a 'crop-out' paint. Crop-outs are born from a pinto-patterned horse, but to the disappointment of the owners, they turned out solid. But the difference between a crop-out paint and a solid horse is that a crop-out paint actually DOES have a paint gene in there, the owner just may or may not know it. It takes a little knowledge and practice to be able to identify a crop-out.

In pinto patterns, all paints carry a certain amount of expressing or suppressing gene. Because all horses start out as a base color (chestnut, bay, black), white is added in. Fully expressed pinto horses have more white; some are so white they almost don't look pinto, like the foal below (notice his ears).

While most paints have a more even balance of both, like the horse below

It does seem like there are a lot of paint horses out there, I personally think there are a lot more crop-out paints than most people would think. The horse below is what some people may or may not recognize as a crop-out paint.

So now, the big question: how do I tell a crop-out pinto from a horse who simply didn't didn't inherit any paint genes? 

A minimally-marked pinto will look, well, like the horse above. Tall white stockings are an indicator of pinto, and also the marking sometimes called, 'bald face', where the face is quite white.

Besides double-dilute horses (cremello, perlino, and smoky white), blue eyes are ALWAYS an indicator of pinto. The horse below has no white markings on her legs, but her face marking is rather large. Even though it doesn't cross over her eyes, it is large enough to mark her as a paint. Plus the blue eyes.

The horses below are very unusual; they doesn't have any particular face marking, but their eyes are blue. It's in there somewhere!

Going back to the stockings, some crop-out paints don't have particularly tall stockings. This is one of the horses I posted earlier:

He is super cool. While I can't be positive about his pinto status, what makes me guess that he is a pinto is because of the way that back left stocking has that jagged edge. Very jagged edges on leg markings, whether tall or short, can give you a clue. I don't know whether this is a hard and fast rule or not. And like I said, I'm not very sure on the above horse.

So, back to the very first question: how does a paint produce a solid horse, and a solid horse produce a paint?

They are actually very different questions. The first question, how does a paint produce a solid horse, is not too hard to answer. Just like other genes, unless more is known about the horse, it is safe to assume that there is a 50% chance of the foal inheriting it. If the foal is born solid, then you need to ask yourself whether they are crop-outs, or whether they actually didn't inherit any pinto gene at all. 

The thing about crop-out pinto horses is that they ARE pintos with pass-alongable pinto genes, just not easily recognizable. One problem with the APHA (American Paint Horse Association) is that they don't admit that crop-outs have pinto patterns, and are then labeled as 'solid breeding stock'. But crop-outs can still produce colored babies, unlike true solid-colored horses. While they can still be registered just as any other paint, they are less desirable.

Back to the other question: how can a solid horse produce a paint? Now that you are more informed, you know the answer: that pinto pattern didn't come from nowhere. One of the parents is a crop-out, who is actually not solid.

Going back to the expressed/suppressed pinto genes, that will have to be another post! I'm having a hard time understanding myself how a supressed pinto gene can be hidden for many generations, and then all of a sudden the suppressed gene is turned off and you have a pinto foal.

Horse Color Genetics: Paint Combinations

One thing that has popped into my head recently is how many different combinations of colors can you have without the horse exploding? There isn't a right or wrong answer to this question; most patterns will collide and make a crazy horse, like the one below. 

That is any pinto pattern, + appaloosa. It is fairly rare, not because it's hard to get, but because horse's in the pinto registry aren't allowed to have any appaloosa relatives, and vice versa. It is more common in miniature horses because both colors are allowed. 

Isn't he gorgeous? Black roan + tobiano. 

The above horse is seal bay + roan + tobiano.

This horse is champagne + tobiano.

Obviously, there are many others, but I chose these because I thought they were particularly pretty.

Horse Color Genetics: Tovero

To review paint markings: T=tobiano, O=frame overo, SPL=splashed white, SB1=sabino.

One fact about paint-colored horses that a lot of people don't know is that there are a LOT of paints who have more than just one kind of pinto gene in their coat. They are called 'tovero', although tovero is a frustratingly broad term, and I'll explain why in a minute. For reference, here is a true tobiano, no other paint genes involved. Just so y'all know, those spots are called 'cat tracks' and are fairly common in tobianos.

Here is a person who is partially mistaken on the horse's color. He does have tobiano, but also a different gene as well. 

Compared to horse #1's markings, this horse is actually very different. First off, I know he carries tobiano because the white crosses over his back and his legs are white (see here to re-reference the definition of tobiano). But one of the rules of tobiano that I don't think I mentioned is that tobiano's always have very predictable face markings; a dark head with a 'normal' face marking. 

Now, the above horse has a white head and blue eyes. I've been learning lately that white eyes almost always indicate some kind of overo gene. Here is where it gets confusing: which overo gene is it? Reviewing, there is frame overo, sabino, and splashed white (read more about the difference's here). There are three options, and I'll walk you through why I think this horse is tobiano + splashed white.  Honestly, I am only guessing on the splashed white, it's only a hunch. 

First off, I know it isn't sabino. Frame and splashed white both sometimes cause blue eyes, sabino does not.

The above horse I've seen many people classify as tobiano. He is very beautiful, and I love his cat tracks. However, even though he displays all of the tobiano characteristics, his irregular face markings and blue eyes give away that something else is there. I'm not even going to guess whether he is splashed white or frame overo.

Something that is really important when breeding any paint to another paint at all is to have them genetically tested for frame overo, to save yourself the heartache of an OLWS foal. Because, in thinking that the horse #2 is just tobiano, they could breed him to another frame overo, and surprise! You have a dead foal. While I've talked a little bit about genes 'hiding', frame overo is one of the easiest to hide in a paint that you may think is just any of the other patterns. Even if you are almost positive of it being just tobiano, I would still test.

Horse Color Genetics: Overo and Lethal White Syndrome

Review: E=black, A=bay, G=gray, CR=cream, D=dun, TO=tobiano, F=flaxen, Z=silver.

The first question you may be asking is, "What is overo?" Overo is a pinto coat color in which the large splotches across the body appear to be rather jagged at the edges. In the color overo, the white never crosses the back, so the horse is mostly whatever is the background color. Can you see the difference between the two horses below? The top one is overo, the bottom tobiano.

Similarly to tobiano, any color can be the background: chestnut, bay, black, palomino, buckskin, dun, roan. In genetics, modifiers like overo and tobiano can be in any combination with other colors. The abbreviation for overo is O. The horse below is a dun overo; see the stripe down it's back? I'm not sure whether it is a dunskin or a bay dun.

Another characteristic of overo is generally they have quite a lot of white on their face, extending past what you might call a 'normal' marking. Usually, when the white covers the eyes, the eye is blue.

Overo is rather strange compared to some of the other genetic color modifiers. Unlike other colors, homozygous in frame overo's do not exist. I will get more into what happens if it is in a minute.

There are several different kinds of overo. All the horses above are called 'frame overo'. The other kinds are splash and sabino; sometimes a horse can receive the different kinds of overo, all mixed in at once. The different overo's are actually all different genes, but the other overo's are still associated with overo.

The horse below is a splash overo. Splash overo's basically look like they have been dipped in white paint. Their legs, face, and sometimes their belly and the bottom part of their neck and chest may be white, although generally the minimum is white legs and a lot of white across the face. The horse below has a lot of white and the fact that he is a splash is very obvious.

Sometimes the fact that a horse is a splash isn't apparent, or people don't know it. If a horse has what is called a 'bald face', which is not an uncommon marking, it might carry the splash gene and they just aren't aware of it. The horse below is splashed white. The abbreviation for splashed white overo is SPL.

Sabino overo is a little confusing, as the exact terminology is not very well established. Generally, sabino horses may have a lot of markings, or very minimal markings. White markings are very lacy, even more so than the frame overo, and may even look a bit like roan. Abbreviation for sabino is SB1. The horses below are sabino. The last horse is very minimal sabino; it might even be sabino and splashed white, I don't know.

For both splash and sabino pinto's, whether they are homozygous or heterozygous might show by the amount of white is on their bodies.

Now, back to why frame overo can never be homozygous.
Scientists are struggling to understand exactly why this happens, but if a foal receives two dominant frame overo alleles, something in the stomach doesn't fully develop all the way. The foal is born pure white, and appears completely normal and may function normal for a little while, but after whatever food runs into where the stomach wasn't developed, it has absolutely nowhere to go. Usually, these foals are put down after not too long; they will eventually (within 48 hours) die of, basically, colic. This is called Lethal White Syndrome, or Overo Lethal White Syndrome (LWS, OLWS).

It is very sad, but it is the truth. It can be very dangerous to breed two overo's together, because if both of the frame overo genes are inherited, well, you get the idea. It is safer to breed an overo with a solid color and pray it inherits the one frame overo gene from that particular parent. It is strange that there are as many frame overo's as there are.
Some owners of stallions who are overo that is not frame will still have their horse tested to make sure that there is no frame overo that they aren't aware of (like a combination of different overo's) and will advertise if their horse has it or not.
If breeding two frame overo's together, the chance that it will have LWS is 25%. It is a pretty basic equation; here are the possible outcomes (keep in mind that both parents would be heterozygous) (these are not taking into account the back color): OO (LWS), Oo, Oo, or oo. The reason there are two is, say, the dominant is from the dad and recessive from mom, and the second would be vice versa.