Basic Rules of Coat Color Genetics

Horse colors and patterns can be confusing — here are some guidelines to get you started.

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Photo of overo Mustangs by Sandysphotos2009

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.

*Aramus, Wayne Newton's homozygous grey Arabian stallion. Note the porcelain white color that's common to mature homozygous greys. Photo by Johnny Johnston

Grey: A dominant gene, grey will always express itself over other color genes if a horse inherits the grey gene. It’s not possible for a horse to carry a recessive (and therefore unexpressed) grey gene, so all grey horses have at least one grey parent.

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.

Trademark Flair, a Pintabian colt with "cat tracks." He was DNA-tested and proven to be homozygous tobiano. He's also extremely unusual because he has one dark leg. Photo courtesy of Flair Park

Pinto: Pinto, not Paint, is the correct term for horses with large splashes of color and white on their bodies. Paint is a registered breed of horse, pinto is a color gene. (Of course there are minimally expressed pintos with little white that may not be obviously pinto until you look more closely or have them DNA-tested.) Pinto is dominant, meaning a pinto horse always has at least one pinto parent and will always show some kind of pinto characteristics, even if it’s not obvious.

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.

An overo Paint Horse. Note that the white markings don't cross over the horse's back. Photo by Sandysphotos2009

Overos often have jagged white markings on a colored background, and the white usually does not cross over the back. Horses that are homozygous for the gene (meaning they carry two overo genes) always develop Lethal White Syndrome and have a non-functioning colon that results in death within a few days of birth. Responsible breeders don’t breed two overos to one another since the risks are high of producing a Lethal White overo foal that will die.

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 perlino, or double dilute, horse. It's hard to believe, but this horse's base coat color is bay with two cream genes applied to it. Photo by Arsdelicata

If a horse inherits two cream genes from its parents, it’s called a “double dilute.” If the base coat color is chestnut, the horse becomes a cremello, and if the base coat color is bay, the horse becomes perlino. A smoky cream is the result of two cream genes applied to black. Double dilutes are very light-colored horses with blue eyes.

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.

A blanket like this is the result of a single appaloosa gene. Photo by Kristin Berkery

Appaloosa markings: Appaloosa spots can appear on horses that have little or no registered Appaloosa breeding (such as the European Knabstrupper breed). In this instance, I’ll refer to appaloosa patterns with a small “a” because I’m talking about the color gene, not the breed of horse.

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.

A "snowcap" Appaloosa mare and foal. Note the lack of spots on their blankets. They are both homozygous for the appaloosa pattern gene. Photo by William Thiel

When a horse inherits two appaloosa genes, it’s homozygous for the pattern and will always produce or sire horses with appaloosa characteristics. However, a homozygous appaloosa often will not have spots at all, instead displaying a solid white blanket on the hips or even a nearly solid white body with only a few colored hairs. These are often called “snowcap” or “few spot” appaloosa horses.

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.

A chestnut Clydesdale with high white stockings and a blaze, commonly called "sabino," but probably not the result of the recently-discovered SB-1 gene. Photo by Kristin Berkery

When a horse inherits the SB-1 gene, it usually has white over large areas of its body, and when it inherits two SB-1 genes, it will usually be at least 90% white. Fortunately the SB-1 gene has no association with Lethal White Syndrome.

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.

 

About Kristin Berkery

Kristin is a freelance graphic designer and writer in Sacramento, California, with a life-long passion for horses. She designs websites and marketing materials for businesses. In her spare time she's active with her daughter and son. See Kristin's online portfolio and LinkedIn profile.

One thought on “Basic Rules of Coat Color Genetics

  1. juliainman1969@gmail.com says:

    Hi I have a colour question for you please. My mare is a homozygous sabino I bred her to a spotted varnish roan Appaloosa. The foal is born a mousey silvery colour with a star and narrow blaze on his head and one white fetlock. I thought he would be coloured due his dams colouring and have a 50% chance of spotting out

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