Equine coat color genetics

Equine coat color genetics determine a horse's coat color. There are many different coat colors possible, but all colors are produced by the action of only a few different genes. The simplest genetic default color of all domesticated horses can be described as either "red" or "non-red", depending on whether a gene known as the "Extension" gene is present <!--switched on?? Capital "E"? How does one phrase this??-->. When no other genes are active, a "red" horse is the color popularly known as a chestnut.<!--does that rephrase still sound accurate??--> Black coat color occurs when the Extension gene is present, but no other genes are acting on coat color.<!--Close enough?? We do still have to explain black before Agouti can suppress it??-->The Agouti gene can be recognized only in "non-red" horses; it determines whether black color is uniform, creating a black horse, or limited to the extremities of the body, creating a bay horse.

Chestnut, black, and bay are considered the three "base" colors that all remaining coat color genes act upon. There are a number of dilution genes that lighten these three colors in a variety of ways, sometimes affecting skin and eyes as well as hair coat. Genes that affect the distribution of white and pigmented coat, skin and eye color create patterns such as roan, pinto, leopard, white, and even white markings. Some of these patterns may be the result of...
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