Now that I’ve started learning about horse color genetics, I really have to think when I’m planning something like a dark bay tobiano on a half Paint horse. I was having enough trouble figuring out what pattern I wanted before I realized that he couldn’t show any homozygous tobiano traits, since he can only be heterozygous for tobiano. This is both exciting and frustrating.
One of the reference horses that I’m considering is this unique Paint filly:
I really like her cool black spotting on her lower legs. When the spots are adjacent to the hoof, this is known as ermine spotting (and occurs on non-pinto horses as well). The markings higher up on the legs are known as distal spotting.
Fortunately, some quick research showed that while distal and ermine spotting are often signs of homozygosity, they are not always. So Liam sporting these cool details would not be impossible. What would be impossible, however, would be if his pinto pattern featured cat tracks.
Cat tracks, also known as ink spots, are small, often roany spots usually grouped on the horses barrel or haunches. These markings are homozygous indicators, so they would not be possible on a Paint x Percheron cross.
I tend to like minimal pintos best, and have planned Liam as a pretty minimally marked tobiano. Happily, the amount of white on a tobiano is not dictated by its hetero- or homozygosity. One might think that a horse with two copies of the tobiano gene would have more white than a horse with only one, but there is no genetic or phenotypic evidence for this.
Basically, even with genetics in mind, there are about a million possibilities for Liam’s pinto pattern. And I’ve collected references for about half of those million. So now I just have to narrow it down and make a decision! As I said, both exciting and frustrating.