Horse Color Genetics: Leopard Complex, Part 2

Review: E=black, A=bay, G=gray, CR=cream, D=dun, TO=tobiano, F=flaxen, Z=silver, O=overo, SB1=sabino, SPL=splashed white, LP=leapord complex (appaloosa).

The first thing you need to know about the leapord complex is that it is an incomplete dominant. I know I've maybe mentioned simple and incomplete dominant before, but here is what it means. Simple dominant means that whether the horse has one or two copies of the gene, it will do the same thing. Incomplete dominant means that if you have one gene, it may look different than the horse with two.

With leopard complex horses, just by looking at them it is easy to determine whether they have one dominant LP gene or two. It is actually more simple than you might think. LP horses with spots are heterozygous (one dominant gene), LP horses with no spots (coats like few spot or snowcap) are homozygous (two dominant genes). 

One other thing that is important to know is that all horses with the LP gene are varnish roan underneath. Remember my last post? Anyway, depending on what pattern genes you get, it probably won't show that much. But if you look at the face of the horse's, you can kind of see the roaning in where there are larger patches of dark. This isn't really true of blanket appaloosa's (you can't see the roaning so much), but the presence of the white hairs to make it roan (varnish roan) will be mostly diluted.

For example:

This horse is heterozygous LP. How do I know that? She has spots! Easy. There is a 50/50 chance she will pass the spots onto her babies.

And this one:

 And this one:

They all have spots! Regardless of whether they are all over, or are only on the blanket (or both!), they only have one dominant gene. What could happen if you bred the next two horses together? (Hint: both are heterozygous, or LPlp)

Here are the resulting options:

Surprised at the last one? The different options for the first two horses to have were: LPLP (homozygous; the first horse), LPlp (heterozygous, the second one), or lplp (homozygous recessive, or not present at all).

Now on to homozygous colors. Review: homozygous means you know the horse has two dominant copies of a certain gene. 

Here are a couple horses that are homozygous:

 There is a lot of white. The first one is a snowcap, and the second one is a fewspot (literally!). These horses are homozygous. If you bred those upper two together, what do you think you are going to get? The baby won't have any spots, unless it is a few spot. 

If you remember back to my last post, the last color I mentioned was varnish roan. Varnish roan is the only LP color that is hard to tell; you may not be able to at all without sending your horse's DNA into a lab.

The last thing you may be wondering is, 'How can I tell what pattern my mare's foal will be?' Well, the tricky thing is, you can't. If it might be heterozygous, you won't be able to tell if it will be leapord or blanket. If it is homozygous, you won't be able to tell if it is few spot or snowcap (pray for a snowcap!).

One last fact that is something scientists only recently discovered. Horses that are homozygous for LP have something called CSNB. This stands for congentical stationary night blindness. A mouthful? It is exactly as it sounds: horses that are homozygous are blind in the dark. Surprised? 

You may say, "but my horse sees just fine in the dark!" I'm sure you know your horse very well, but thing is, it probably doesn't. But he doesn't know that. Can you see in the dark? Not very well. Same thing with him. If you couldn't see in the dark, and then someone told you that everyone but you sees in the dark, what would you do? You've always been that way, and there isn't anything you can do about it.

 He has always been that way, and always will be, and he won't know anything different. He has developed ways to get around pretty well in the dark on his own. There isn't anything you can do about it, and I wouldn't really say it is a bad thing to have either. I wouldn't not breed my two homozygous horses together to prevent it, even though it is inevitable to happen.

In conclusion, if you want a spotty horse, breed a  homozygous LP horse with a homozygous recessive. That way, you will have lots of color! In the Appaloosa and Pony of America registry, if you cross with certain breeds, then it is still eligible for full registry. These crosses include: Quarter horse, Arabian, Morgan, and Thoroughbred. Some spotted horse breeders keep these breeds so they can make more color and crazy spots. 

Horse Color Genetics: Leopard Complex, Part 1

Review: E=black, A=bay, G=gray, CR=cream, D=dun, TO=tobiano, O=overo, F=flaxen, Z=silver, SPL=splashed white, SB1=sabino.

In this first post, I'm going to show you the different coat colors, and then get into the genetics and how they work in the second part of the leopard complex.

The genetics to the appaloosa complex are very tricky to understand, and I'm still trying really really hard to understand more about how the pattern genes (modifiers to the appaloosa gene) work.

The correct term for appaloosa complex is leopard complex. LP. This gene is seen in the breeds like the Appaloosa, Pony of America, Knabstrupper, Colorado Ranger, and Miniature horses. When I refer to appaloosa in this post, I mean spotted horses, not necessarily the breed. The breed is capitalized.

When a horse inherits the LP gene, the first thing you need to understand is the characteristics that they receive. Regardless of the pattern genes, whether they got one or two dominant LP genes, the traits they will always have are:

Mottled skin (sorry for the gross picture!)

The sclera of the eye shows (the white part)

And lastly, vertically striped hooves.

A horse will have these three things whether they have one or two dominant LP genes. Some horses with LP may or may not have mottled skin on their muzzle, but their private parts will be spotty.

So, as in other color modifiers, there is always a base coat. To make things easy, I'll use chestnut, ee,aa. Remember, no matter what markings or color, they will all have the LP traits. Starting on down the list, I'll begin with the colors, beginning with the easiest to identify. 

The horses below are leopard appaloosa. Leopard appaloosa's have spots all over them, and the name is easy to remember. The size of the spots doesn't matter (well, a little), nor the color. Out of these three horses, which one is not an appaloosa?

If you guessed the third one, you were correct! This guy is flea-bitten gray. Here is the different post on that; gray horses don't have any LP traits.

The first horse's base coat is bay (see the little black wisps in her mane?), and the second horse's base coat is black. 

The next color is a blanket appaloosa. Blanket appaloosa have white bums; the white can be only a tiny little section, or it can nearly cover the entire horse! Technically, on the white there can be spots or no spots, but for the sake of genetics I am going to say that blanket appaloosa's always have spots. Aren't they pretty? The first is a bay blanket, the second is a buckskin blanket.

The next color is snowcap blanket. Snowcap blankets have a blanket, but without spots. It should be pure white. Genetically, snowcap and blanket are different.

The next color is few spot. Few spots are a bit uninteresting to look at, but they are important to the LP gene. Few spots may look a bit like cremello, but have LP traits. They can literally have enough spots to count on one hand, or a little more than that. Some can have roaning associated with the LP gene in their 'corners'.

Another color associated with the LP gene is called varnish roan. Varnish roan is different than normal roaning. You may or may not be able to see the difference from the first two horses and the last horse, but varnish roans carry the LP gene and have those traits.

Those are the basics. There are others that you may read about, but they are pretty rare. These are the most common and make the most sense to explain.

Horse Color Genetics: Dun

Review: E=black, A=bay, G=gray, C=cream.

The next color is dun. What is dun? A dun horse is a horse that receives special markings through its genetic code. Dun horses always posses a very clear dorsal stripe, or a black stripe that runs across their spine. Dun horses commonly have faint stripes on their legs, and sometimes a faint dark shading across their shoulder blade. Duns always have a darker mane and tail than their base coat; whether the mane and tail is black depends on whether they also have an E gene. The only exception to this rule is a palomino dun, whose mane and tail will still be white, or cremello dun. In the second picture, the horse has a dark bar along his shoulder; some duns may or may not have this. There are lots of duns with dorsal stripes below!

The dun gene, or D, is a simple dominant, meaning that whether the horse is homozygous dominant or heterozygous, it will effect the horse in the same way. When I say almost, I mean that depending on the base coat, it will vary. It does not necessarily effect different colors in the same way; the original color without the D gene will still show through.

The D gene has a lightening effect on any coat. Usually combined with a chestnut horse (ee, aa), black horse (E?, aa), or a bay horse (E?, A?), the base coat will show through, but if it is a bay horse (E?, A?), the rules of how it goes can be confusing. The dun gene pushes any existing black to the edges, similar to to the A gene; however, it usually leaves the face and legs darker.

There are several different technical terms within dun, depending on what the underlying coat is. The most common color is 'classic dun', or sometimes 'bay dun' or just 'dun'. Bay dun (E?, A?, D?), when the D gene is added, dilutes the dun to a very light color. This color is usually the same or nearly the same as a buckskin, although there is a clear difference; buckskin by itself usually doesn't have the dorsal stripe. The horse below looks an awful lot like a buckskin, right? But he is actually a bay dun. He is so cute!

To make matters more confusing, there is such thing as a buckskin dun. This horse's code will look something like this: E?, A?, Cc, D?. This means that it was a bay, then diluted to buckskin, then diluted further to a dun. Buckskin bay, or dunskin, is more of a bright golden, while a bay dun may be slightly duller, more brown.  If you aren't sure, you may need to have your horse genetically tested. If there is ever any question as to which, if you know about the parents that could help. Remember: buckskin is the result of a bay with a cream gene. If there is no cream gene in either of the parents, then you know it is a bay dun. See how much more golden he is? Much less brown.

Chestnut dun, or red dun, turns the horse's chestnut coat to a lighter, more rosy shade. Remember, chestnut horses are recessive black, so the mane and tail are not black. They will turn a darker shade than main coat though. A clear dorsal stripe still shows, but it will probably be dark red instead of black.

Black dun horses are called grullo (or grulla (pronounced Grew-yo, or Grew-ya) depending on who you talk to). Grullo horses are black horses with the dun dilute; they turn almost a blue roan color, or sort of grayish with a dark head and dun characteristics. 

Dun can also effect horses with other color genes, including pinto, roan, palomino, among others. I won't post pictures of them all; basically dun will always lighten a color, and add a dorsal stripe. The horse below is a tobiano dun.

There is something else called 'countershading' that can sometimes be confused with the D gene. Countershading looks like a dorsal stripe, but it won't be very clear, or might go halfway up the back, or may be a thicker line. A dorsal stripe should be very clear and straight, like someone took a juicy dark marker and ran it up their back. If the stripe is kind of thick with not clear edges, then it is countershading. The horse below is so close! But....it isn't complete. He is not a dun. The stripe isn't clear, and it doesn't go up the back all the way.

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.

Horse Color Genetics: Tobiano

Review: E=black, A=bay, G=gray, Cr=cream, D=dun
Tobiano, for those of you that don't know, is a horse color in which the horse is two different colors in large splotches. The generic term for two-colored (or sometimes three-colored) horses is pinto, but tobiano is a more specific term. Each specific pinto term is defined by different genes.
To define a tobiano: any color combinations with white; the patches will be smooth, with white or color changing across the back between the withers and the top of the tail (like the horse below). Tobiano horses also generally have the darker color across their face and chest, like a shield. Tobiano is the most common pinto color; the amount of white will vary. Markings on the face may or may not be present, but will resemble solid-colored horse's markings on the face (star, stripe, blaze, etc.). If crazy markings are on the face, then another different pinto gene may also be present. Usually white below the knees and hocks (hocks are like the knee for the back legs). Tobiano's may or may not have blue eyes, any horse can have blue eyes.

The tobiano gene (or T, or TO) will show up, whether the horse is homozygous or heterozygous. The amount of craziness going on, or the amount of white, usually depends more on the parent from which it inherited the TO gene. For example: a tobiano horse with not very much white and is homozygous, bred with a recessive TO gene (to), will probably result in a foal with minimal white, like the tobiano parent.

Like I said before, any color can be tobiano. Chestnut, black, and palomino; also bay and buckskin. Bay and buckskin tobiano's are tri-colored horses, because their manes and tails are black, while their bodies are colored and white. However, horses with the cream gene (palomino, buckskin, dunskin) may produce foals that carry the TO gene, but it isn't apparent or is very washed out (a cremello horse's pattern wouldn't show). Sometimes the TO gene will block out other modifying genes. Other stranger, but still possible, colors, are roan and dun. The below horse is a roan tobiano.

Foals that are born with tobiano coloring will stay this way their whole lives. The color may vary a little once they shed out their baby fuzz, but the markings will always be the same. The only exception to this would be if they inherited a G gene, in which they would inevitably gray out, and their markings would no longer be visible unless they never grayed out all the way.

Here is Pepper. He follows all the rules for tobiano: white across the back, white below the knees and hocks, a dark head and chest, and a 'normal horse' marking on his face.