Equine Base Coat Red/Black Factor
Equine coat color is built on one of two possible base pigments: red or black. The extension gene controls the production of this base pigment (red or black). All of the coat colors we see today, from white to black, sorrel to grey - every single one of them begins with either a red or black base pigment. All horses will have the genetics for black or red pigment, regardless of their physical appearance. There are a number of dilutions patterns and modifiers which a horse can carry that affect the base pigment of a horse.
Horses that are bay, black, grullo, buckskin, black/blue roan, etc. are black pigmented horses that carry at least one copy of the Black Factor (E) allele. The black (E) allele of the extension gene is dominant and causes a black pigmented base both in the heterozygous (Ee) and homozygous (EE) state. A horse that is heterozygous for Red/Black Factor means that it carries one copy of the black allele (E) and one copy of the red allele (e). A horse that is heterozygous for red/black factor can pass on either red or black pigment to its foals. A homozygous black (EE) horse means that it carries two copies of the black allele (EE). A homozygous black horse will always produce black based foals regardless of its mate.
Horses that are chestnut or sorrel, palomino, red dun, red roan, etc. are red pigmented horses and must carry two copies of the Red Factor (e) allele. The red (e) allele of the Extension gene is recessive and will only cause red pigmentation when the horse carries two copies of this allele; this is referred to as Homozygous red (ee). Therefore, a red based foal results when both parenst have passed on a copy of the red (e) allele.
Animal Genetics offers DNA testing for the extention gene effecting the Red / Black base coat color of a horse. The genetic test verifies the base coat color and presents results as one of the following:
|E/E||Black||Only the black factor detected. The horse tested homozygous for black pigment. It cannot have red foals regardless of the color of the mate. The basic color of the horse will be black, bay or brown unless modified by other color modifying genes.|
|E/e||Black||Both black and red factors detected. The horse tested heterozygous for the red factor. It can transmit either E or e to its offspring. The basic color of the horse will be black, bay or brown unless modified by other color modifying genes.|
|e/e||Red||Only the red factor detected. The horse tested homozygous for red pigment. The basic color is chestnut or sorrel unless modified by other color modifying genes.|