Basic Rules of Coat Color Genetics
Horse colors and patterns can be confusing — here are some guidelines to get you started.
by Kristin Berkery
orses come in all kinds of colors and patterns, and even the most experienced horse enthusiasts will occasionally come across something so unusual that it stumps them. (Thank goodness for DNA testing.) But there are some basic rules of coat color genetics that you can always count on. If you have additional ones to share, please comment at the bottom of the article.
Some horses are homozygous grey, meaning they carry two grey genes and can only pass grey on to their offspring. Since grey is dominant over other colors, a homozygous grey will always produce or sire grey offspring. Homozygous greys can be found in Lipizzans and Arabians, among other breeds.
Grey is not actually a color, it’s a process of depigmentation, or fast aging, of the horse’s base coat color. A foal that’s destined to be grey is typically born bay or chestnut and then becomes grey over time. Sometimes the process is very slow, other times it happens quickly. Horses can grey in different ways too — some are a very dark steel grey that lightens gradually, others turn a rose grey (almost pink) color, and still others become heavily dappled grey. Aged horses can become porcelain white, which often happens with homozygous greys, while others become heavily fleabitten, a process where the depigmentation reverses and the horse’s base coat color begins to return in the form of “freckles.”
Chestnut: A recessive gene, chestnut requires that both parents pass a chestnut gene to their foal in order for it to be chestnut. If you breed two chestnut horses to each other, you are guaranteed a chestnut foal.
The two most common types of pinto are tobiano and overo. Tobianos almost always have four white hooves — the main exceptions tend to be Miniature Horses and ponies (like Shetlands), which occasionally will have one dark leg, but almost never two dark legs. Tobianos tend to have smoother, rounder areas of color and the white will typically cross over the back at some point.
Some horses are homozygous tobiano, meaning they carry two tobiano genes and only produce or sire tobiano foals. Homozygous tobianos can sometimes be identified by lots of “cat tracks,” or small, round spots of color anywhere on their bodies.
Grey is not actually a color — it’s a process of depigmentation of the horse’s base coat color.
Cream: The cream gene is what gives us palominos, buckskins, smoky blacks, cremellos, perlinos, and smoky creams. When applied to chestnut, the cream gene produces palomino; when applied to bay, it produces buckskin; and when applied to black, it produces smoky black (but often appears brown).
A dilute horse will always have at least one dilute parent, even if neither parent looks like it carries a dilute gene. Because smoky blacks can look like seal brown horses, their owners may be unaware they carry a cream gene until they produce or sire a dilute-colored foal.
Similar to the cream gene, the appaloosa gene affects a horse’s color depending on whether the horse carries one or two appaloosa genes. But the appaloosa gene differs from the cream gene due to the wide spectrum of how it can affect a horse’s coloring. When a horse inherits a single appaloosa gene, the horse’s appaloosa coloring can range from a few white hairs on the body to a loud leopard pattern, and some patterns don’t express themselves until a horse is an adult.
Sabino: The best known sabino markings are high white leg markings and wide blazes, like on the Budweiser Clydesdales. But sabino markings can also include extensive spots and roaning on the belly, chin, jaw, throatlatch, and other areas. Surprisingly, recent research has shown that the gene responsible for sabino markings, SB-1, may not be found in Clydesdales and Arabians, another breed known for lots of “chrome.” Instead, it’s thought that Clydesdales and Arabians owe their sabino markings to a combination of other genes that haven’t yet been identified.
These are some of the most common coat color “rules” you can rely on in horses, but there are many other uncommon colors and combinations. Lesli Kathman has some great horse color articles at EquineTapestry.com. Read about a dunalino, a horse with both palomino and dun genes, and the lovely champagne color here at ilovehorses.net.