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.