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: Calculating Possible Outcomes

When determining possible outcomes for foals, almost everyone knows about the coat color calcuator, here. Lately, I've been practicing figuring the results without it, because I would like to know them off the top of my head.
To start, it's good to have a definite color genome because without it, the numbers are much more confusing. I'm still working on how to solve that.
Let's start with an easy one:

Ee aa + EE Aa

When starting on calculating, always work from left to right, and write it down with a pencil so you can erase the numbers to make them smaller as you get more detailed.
To solve the question, use common sense to know that the horse will always be black-based; the horse on the right is homozygous dominant for black.
So now the question: will the horse be black, or bay?
We know from the horse on the left that at least one agouti gene will be recessive. The other one is 50/50, so therefore, the outcome is 50% black, 50% bay. The possible genomes are EE aa, Ee aa, EE Aa, or Ee, Aa. The first two were for a black horse, the second two were for a bay. Even odds, making:

50% Black
50% Bay

Let's change it up:
Ee Aa + Ee Aa

Only look at the extension status to start with. The possible outcomes for just that are: EE, Ee, Ee, or ee. Why did I do Ee twice? Because you can take into account that the dominant gene could come from either one. You could change the second Ee to eE if it helps you remember which one comes from which.
Now, looking at those, 3/4 of those outcomes make a black or black-based horse. So we have:

75% black (we'll change that later once we find out about agouti)
25% red

Using the same technique as before, the possible outcomes for the agouti status would be the same: AA, Aa, aA, or aa. 3/4 makes a bay horse.
To apply this to the equation above, remember that the red status shouldn't change. That is solid; we are only applying this if the foal was black. So the real question is what is 3/4 of 75%?

Think back to math class; to figure this, multiply the 75 times 3, then divide by 4. That leaves you with 56.25; those are the final results for bay. But obviously 56.25 + 75 + 25 don't add up to 100; you now need to change the black outcome. Add up the red status plus bay, then subtract that number from 100 to get the final answer for black. That number is 18.75. Here are the final results:

56.25% Bay
25% Red
18.75% Black

Now if you add on more modifiers and dilute genes, the genetics aren't as hard as you think. Generally you just divide each number in two. For example, let's use what we have above but add in that one parent has one copy of the cream gene. Going back to the parents, their genome's now look like this:
Ee Aa Cc + Ee Aa cc (one parent is recessive for cream, and generally you wouldn't show it, but I put it in so you could see).

To calculate, first do all the above steps and you would come to the same conclusion as the above, but without the cream. Now that you've done those steps, you can add in cream. For just the cream status, the possible outcomes are: Cc, cc. Just those two. The first one has cream, the other doesn't. Because it's 50/50, all you have to do is individually cut each color in half and add in whatever that color would be with cream. Like this:

28.125% Bay
28.125% Buckskin
12.5% Red
12.5% Palomino
9.375% Black
9.375% Smoky Black

I used a calculator for those smaller numbers, but once you get a little more accustomed to doing these, there are a lot of repeating numbers such as 75, 50 25, 12.5, 37.5, you get the idea. If you compare these numbers to the online coat calculator, the only difference is that they round up on the small numbers to change 28.125 to 28.13 and 9.375 to 9.38.

Horse Color Genetics: Appaloosa Pattern Inheritance

Going back to the question that started it all, and what I determined. Can my solid black horse Chocolate with appaloosa breeding produce an appaloosa foal when bred to another solid horse?

The answer is no. Not to another solid horse, and I'll explain why.

The LP gene needs the master switch turned on. Without the master switch, none of the pattern genes work. BUT....that does not mean that Chocolate does not have pattern genes.

Both of Chocolate's parents were blanket appaloosas. But both were heterozygous for LP, and Chocolate inherited both of the recessive genes. How do pattern genes work?

You need to imagine each LP allelle seperately. Linked to each allelle are two different pattern gene options. Imagine the bunkbed, back from the KIT gene post. These mini-patterns that are linked to each main LP allelle can be either turned on or off, even if both of the main LP genes are recessive. Sort of like how a pillow and a blanket could be in the bunkbed whether someone is using them or not. I picture it like this:

LP patn/patn1     LP patn/patn1

The above shows each LP allelle seperately, with both pattern genes turned off. The first one is for leopard, the second is for blanket.

So that means that Chocolate, even though she is solid, could carry pattern genes, but the master switch is turned off. How does this translate to breeding?

Most appaloosa's carry pattern genes, so not having a pattern gene is not really a big deal. If Chocolate didn't have any pattern genes, but if I bred her to a homozygous appaloosa, then she would still probably throw a colorful foal. That is because any pattern genes the foal needed would come from the father.

This is not always the case, but I really would like to know how any genes Chocolate has could effect what LP pattern the foal could have. The stallion that I'm looking at is this guy:

He is homozygous LP, so the foal would certainly be heterozygous LP. But, within the heterozygous range, there are three pattern options: leopard, blanket, or varnish roan.

I would be so disappointed if it came out varnish roan, but because I've seen a lot of this stallion's offspring, and of the two foals Chocolate has had are super colorful, I am fairly certain that there is no chance the foal would not get no pattern genes. No pattern genes equals varnish roan, FYI.

Now, the question I am dying to know: which of the two remaining patterns is most probable?

The frustrating answer? There is no way to know. The information I want doesn't exist. Scientists are trying really hard to understand how appaloosa pattern inheritance works, but it is really hard to trace. My information that I wrote about above could be proven completely wrong in 10 years.

As a side note, one of Chocolate's foals was from this same stallion, JKB Quick Draw McGraw. The filly was a gorgeous black leopard. So I know that that is very likely to happen again. This is not the exact filly, but it did look a lot like this: