Equine coat colour 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 genes. The combination of the extension and agouti loci determine the base coat of a horse.Bay is the original "wild type" color of horses. Ancient remains of horses were tested to be of bay base coat color. The Dun test was not available at the time, but those horses were also dun. (EE AA DD)

Red horses were created with a modification of the extension locus. Dominant extension mutated into a recessive form. When the horse is homozygous for recessive extension (or ee), the horse's base coat will be red. Black horses were created with a modification of the agouti locus. Dominant agouti mutated into recessive form. In the presence of dominant extension (at least one copy of E. So, Ee or EE), a homozygous recessive agouti (or aa) horse will be black based.

There are a number of dilution genes that lighten these colors in a variety of ways, sometimes affecting skin and eyes as well as hair coat, including cream, dun, pearl, champagne and silver dapple. 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 a single gene, others may be influenced by multiple alleles. Finally the gray gene, which acts differently from other coat color genes, slowly lightens any other hair coat color to white over a period of years, without changing skin or eye color.

Much of the modern understanding of equine coat color genetics is owed to the work of Dr. Ann T. Bowling of the University of California, Davis and of Dr. Phillip Sponenberg of Virginia Polytechnic Institute. Modern discussions of horse coat color genetics are based on the distinction between "red" and "non-red" coats, a factor determined by a single gene. More detailed discussions of coat color all refer to the differing effects of separate genes on these "base" coat colors.

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