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!