This post first appeared on Feburary 23, 2012
More information keeps coming in from the new Splashed White tests being offered by UC Davis. Horses that have tested positive for the second version of the splash mutation (SW2) have been identified. Only a few have been made public, but links to those have been added to the Splashed White Project page*. So far, the positive results have been consistent with the rumor that the SW2 mutation is present in the Gunner line of Paint Horses.
For many, the biggest surprises with the new tests have been how many horses have tested negative. I had suspected that might happen, because I knew that blue eyes were not a reliable indicator that a horse could or would produce the classic pattern. Finding horses without the classic pattern testing negative was something I expected. What I didn’t expect at all was to find horses that tested negative with the classic pattern. And now that is exactly what has happened.
Those that have read Jeanette Gower’s book Horse Color Explained may remember the Australian splash line of Bald Eagle. Several horses from this family are pictured in the book. They have classic splash patterns, but so far, they have all tested negative for all three genes. What is even more interesting is that, speaking to breeders, it is clear that this particular family show this pattern with just one copy of their gene. Unlike the SW1 mutation, which presents as a classic pattern when it is homozygous, the Bald Eagle horses have the classic pattern – and produce it – with only one gene. One breeder stated that it was thought that the color was homozygous lethal, which is what is thought to be true of SW2 and SW3.
With each new pattern test, it becomes more clear that there are a lot more pattern mutations that previously understood. Because the Bald Eagle line is a sizable family, it seems likely that their mutation – which may be unique to them – will be identified in time. But the discovery that they look so much like the SW1 horses, yet have some other mutation, is another sign that we probably have a lot more patterns than was previously thought, and a lot of them probably look a lot alike.
*The Splashed White Project was made obsolete when social media groups made it easier to share photos and testing results, so it was not moved with the archives to this new blog site.