Model Horse Reference -- Horse Coat Color Genetics

Chart of Color Alleles

The following chart lists known genetic loci and alleles as well as hypothetical loci that affect coat color in horses.

* = indicates a theoretical locus and alleles, and gene action.

Locus	Category	Alleles	Description	Action
Basic Color Loci The two Epistatic Loci that determine the most basic underlying color of the horse, to which all other loci are modifiers (according to current studies).
Agouti/Bay	Basic	A+=Wild Type Bay A=Common Bay a=no effect	Modifier color that limits black to the points. This allele has no effect if it is homozygous recessive or the horse is not genetically black. Hypostatic to E (extension) or black/red locus.	Multiple Dominant/ Epistatic
Extension/ Black or Red	Basic	E^D=Dominant Black E=Bay e=no effect	Determines whether or not a horse is capable of producing black or red pigment. Epistatic to the A (Agouti)locus.	Multiple Dominant/ Epistatic
Dilution Loci Genes that lighten or dilute the pigment within the coat or hairs.
Cream	Dilute	C^Cr=Cream C=no effect	Causes chestnut to become palomino, and bay to be buckskin when heterozygous. Homozygous form causes "cremello", or white, with pink skin and blue eyes.	Partial Dominant
Champagne	Dilute	Ch=Champagne ch=no effect	Causes Black to lighten to light brown, red lightens to yellow. Also lightens the skin color, causing "pumpkin" colored (dark pink) skin, often with small grey spots, and amber or hazel colored eyes.	Simple Dominant
Dun	Dilute	D=Dun d=no effect	Lightens most of the colors on the body, including black. Black becomes Grulla, Bay becomes Yellow Dun (similar to Buckskin), Chestnut becomes Red Dun. Allows for expression of primitive dun-factor markings such as dorsal stripes, leg bars etc.	Simple Dominant
Silver Dapple	Dilute	Z=Silver z=no effect	Dilutes black pigments to flaxen or chocolate brown.	Simple Dominant
Modifying Loci Genes that somewhat modify or alter the final color, but without fundamentally changing the color.
Pangare	Modifier	Pa=Pangare pa=no effect	Causes "mealy" golden colored areas, most notable on the face and muzzle, girth, flank, dock and underside areas.	Simple Dominant
Sooty*	Modifier		Causes dark sooty areas on the coat. Dappling will be more pronounced on sooty colors.	Unknown
Flaxen*	Modifier		Light cream or flaxen colored mane and/or tail on horses that are chestnut.	Unknown Thought to be Recessive
Masking Loci Genes that mask or largely "cover up" the underlying basic color of the horse.
Grey	Masking	G=Grey g=no effect	Causes a pattern of greying that is progressive with age	Simple Dominant
Dominant White	Modifier	Wh=White wh=no effect	Causes a horse to be white color in it's heterozygous form. White, has pink skin with small dark spots in the skin. Believed to be lethal when homozygous.	Simple Dominant/ Lethal
Roaning Loci Loci that cause white hairs to occur within the coat, without underlying pink skin.
True Roan	Roaning Pattern	Rn=Roan rn=no effect	Causes Roan coloring over the body, with non-roaned head and lower legs when heterozygous. Believe to be lethal when homozygous	Simple Dominant/ Lethal
Frosty Roan*	Roaning Pattern	Fs=Frosty fs=no effect	Causes roaning in the mane tail, over bony areas and often over the topline	Simple Dominant
Rabicano* (White Ticking)	Roaning Pattern	Rb=Rabicano rb=no effect	A roaning pattern often known as "roan in the flanks". Amount of roaning may vary, and typically roan patches will also be found behind the ears, in the armpits, under the dock, and at the tail head.	Simple Dominant
White Spotting Pattern Loci Genes that cause a horse to have white patches on the body with underlying pink skin.
Tobiano	White Spotting Pattern	To=Tobiano to=no effect	Rounded patterning of spots, typically featuring four high white legs, rounded shaped spots, white crossing over the top of the horse, often with "normal" face markings.	Simple Dominant
Frame (Overo)	White Spotting Pattern	Fr=Frame fr=no effect	Irregular white spots, usually accompanied by a blaze or bald face, white commonly found along the horse's sides. The white does not usually cross the back between the withers and tail when heterozygous. Believe to be lethal when homozygous.	Simple Dominant/ Lethal
Sabino (Overo)	White Spotting Pattern	Sb=Sabino sb=no effect	Irregular white patches, usually accompanied by a blaze or bald face extending onto lower lip. Extensive white on the legs is common, as well as odd white patches on the legs. White tends to be more extensive along the underside, with patches commonly found in the girth, flank and throatlatch areas.	Simple Dominant
Splashed White (Overo)	White Spotting Pattern	Spl=Splash spl=no effect	Commonly found as large white patches, most commonly found over the head, chest and forelegs.	Simple Dominant
Leopard Complex (Appaloosa)	Spotting Pattern	Lp=Spotted lp=no effect	Includes the entire leopard complex of appaloosa spotting; body spots, white over the hips, white body with dark spots and various combinations thereof. Homozygotes may show more white than heterozygotes.	Simple Dominant

Keep in mind that all horses have alleles at each and every locus. While it is possible that a horse could be carrying alleles that cause it to be grey, dun, roan, tobiano, frosty, and cream all at the same time, most horses carry recessive (no effect) alleles at many of the loci outside of the basic Extension and Agouti loci.

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