The Basics

Horse genetics can become confusing and take awhile to understand. Here is a basic guide to understanding horse color genetics. Use command+f to find any gene on this page.

Let’s Bake a Gene Cake!

Now gene cake doesn’t sound like it would taste all that good but it’s a good metaphor to use when explaining horse coat colors. To change the color of your “cake icing” (the coat color) you need to add different “drops of color” (the alleles). Some alleles will change the overall color of your horse but others add white markings, think of them as the “sprinkles” on top of our metaphoric cake. All horse colors all begin to form from some basic genes. Lets Get Mixing!

E & A Genes

The Extension (E) Gene

The “E” gene is referred to as the extension gene and determines if there is black pigment present (Ee or EE). Without one “E” your horse will not express black pigment (ee). The presence of only two “e” genes means your horse doesn’t have black pigment.


Ee or EE shows black hair pigment

ee will not show black hair pigment

The Agouti (A) gene

The “A” gene is referred to as the agouti gene and is responsible for the distribution of black hair. Having at least one present “A” gene and no present “E” genes means your horse will be a shade of chestnut (Aa ee, AA ee). Having only two “a” genes and no “E” gene means your horse will also be chestnut (aa ee).

In Eqcetera the “A” gene has a few variations to account for different shades of chestnut and bay (see bay below).

A: Red chestnut or bay

At: Standard chestnut or seal bay

A+: Light chestnut or wild bay

If two of the “A” variations are present the more dominant “A” gene will be what is expressed.

A: Expressed over At

At: Expressed only with other At

A+: Expressed over A and At


aa ee, Aa ee and AA ee will show chestnut coat color.

Variations of the “A” gene will display different shade of chestnut or bay.

The “E + A” Coat (Bay)

The “E” and “A” genes combined make a new coat color,bay! As stated above the “A” gene determines where black pigment will be distributed. All bay coats will have at least one “A” and one “E”.


Aa or AA will distribute black pigmented hair if at least a single E gene is present.

aa will not distribute black pigmented hair

Aa Ee, AA Ee, AaEE, AA EE, will all result in bay coated horses.

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