Equine coat color genetics


 * ''For less technical information on horse colors generally, see Equine coat color

Equine coat color genetics determine a horse's coat color. All horses begin genetically with a base coat of "red" (chestnut) or "black." Then, additional alleles or "modifiers" act upon the base colors to create all other equine coat colors. This base color is designated as "e" for the recessive red allele and "E" for the dominant black allele.

Coat color alleles affect melanin, the pigment or coloring of the coat. There are two chemically distinct types of melanin, red–yellow phaeomelanin, and the brown–black eumelanin. All coloration genes in mammals affect either the production or final effect of these two chemicals.

Genes appear in sets of two, with each individual gene being called an allele. When a gene set contains two copies of the same allele, it is called homozygous. When it has two different alleles, it is heterozygous. For a recessive gene to be expressed, it must be homozygous, but a dominant gene will be expressed if it is heterozygous or homozygous. The difference is that a horse with a homozygous dominant gene will always pass it on to their offspring, while a horse with a heterozygous dominant will statistically only pass on the gene 50% of the time.

Background information
There are currently two major theories of equine coat color genetics: those based on the work of the late Dr. Ann T. Bowling of the University of California, Davis and of Dr. Phillip Sponenberg of Virginia Polytechnic Institute. These theories overlap, and have more similarities than differences.

The terms Alleles and Modifiers are used interchangeably in this article. An allele identified with a capital letter is a dominant gene, one identified with a lower-case letter is a recessive gene.

The genetics of white horse markings are not yet fully understood but are probably influenced by multiple alleles.


 * ''Note: For a quick lesson in genetics and heredity, see the articles on alleles or other footnoted tutorials on inheritance.

Lethal roan question
Hintz, H. F. and VanVleck, L. D., published 1979. "Lethal Dominant Roan in Horses". Journal of Heredity, 70:145-146. This study, based on percentages of roan foals thrown by roan parents, popularized the idea of Lethal Roan Syndrome. The study did not include direct genetic analysis and assumed fetus absorption preventing birth. Similar studies suggested that roan-to-roan breedings were lethal because the resulting embryos were absorbed. This was thought to be true because homozygous roans, horses that carried two alleles for the roan characteristic, were rare.

A recent genetic study of roans by Dr. Bowling refuted Hintz and VanVleck’s inferences. Using genetic analysis, Dr. Bowling found several homozygous roans and no evidence of a Lethal Roan Syndrome.

Sources and external links

 * DreamView Farm Horse Genetic Color Guide - Main basis for this article. Used with author's permission.
 * Horse genetics page from the UC Davis Veterinary Genetics Lab
 * Bowling, Ann T. "Coat Color Genetics: Positive Horse Identification" from Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis.
 * Horse color genetics by Dr. Sponenberg
 * D. Phillip Sponenberg, DVM, Ph.D. Virginia-Maryland Regional College of Veterinary Medicine Virginia Tech, Blacksburg, VA 24061
 * Grullo and roan color education- Cedar Ridge Quarter Horses
 * A discussion of equine roan color genetics - Hancock Horses
 * "In the Genes." Quarter Horse News, Dec 15, 2004
 * Equine color genetics information - Provides clear explanation; a good source for the beginner. Contains info on "possible lethal roan".
 * International Champagne Horse Registry
 * About Horse Color, Genetics, & Markings From The ULTIMATE Horse Site. Includes information on common & rare horse colors, includes photos.

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