Equine Coat Color Genetics - Alleles and Effects

Alleles and Effects

Locus Alleles Effect of combined pairs of alleles
Extension (E) E
e		 EE or Ee: Horse forms black pigment in skin and hair.
ee: Horse is chestnut, it has black pigment in skin, but red pigment in hair.
Agouti (A) A
a		 Agouti: Restricts eumelanin, or black pigment, to "points," allowing red coat color to show on body. No visible effect on red horses, as there is no black pigment to restrict.
AA or Aa horse is a Bay, black hair shows only in points pattern (usually mane, tail, legs, sometimes tips of ears).
aa: No agouti gene. If horse has E allele, then horse will be uniformly black.
Cr Cr
C		 Cream gene The cream gene is an incomplete dominant.

CC: No dilution factor, horse is fully pigmented. (UC Davis abbreviates as N.)
CCr: Single dilution factor (heterozygous dilute) results in Palomino, Buckskin or Smoky Black. Red pigment is diluted to gold with cream to white mane and tail; black pigment is not visibly altered on black points or black horses, though genetic testing can reveal "smoky black" coloration. (UC Davis abbreviates as N/Cr.)
CrCr Cremello or Perlino: Double dilution factor (homozygous dilute). Red pigment is diluted to a pale cream. Black pigment is diluted to a reddish shade. Skin and eye color are also diluted, skin is pink and blue eyes are common with double diluted creams. (UC Davis abbreviates as Cr.)
D D
d		 DD or Dd: Dun gene Another dilution gene. Horse shows a diluted body color to pinkish-red, yellow-red, yellow or mouse gray and has dark points including dorsal stripe, shoulder stripe and leg barring.
dd: Horse has undiluted coat color.
Ch Ch
ch		 Champagne: A rare but dominant dilution gene that creates pumpkin-colored freckled skin, amber, greenish, or blue eyes, and gives a bronze cast to hair. The skin surrounding the eye must be pink with freckles in adulthood.
ChCh or Chch: Champagne dilution evident (See Genetic Formulas Chart below.)
chch: No champagne dilution
Z Z
z		 ZZ or Zz: Silver dapple - Dilutes eumelanin or black pigment. Converts black to brown with white mane and tail or results in silver coloring.
zz: No silver dapple.
Prl Prl
prl		 Pearl: A new rare recessive dilution gene that looks very much like Champagne. The Pearl gene is sometimes referred to as the "barlink factor." One dose of the mutation does not change the coat color of black, bay or chestnut horses. Two doses on a chestnut background produce a pale, uniform apricot color of body hair, mane and tail. Skin coloration is also pale. Pearl is known to interact with Cream dilution to produce pseudo-double Cream dilute phenotypes including pale skin and blue/green eyes.
PrlPrl or Prlprl: No pearl dilution.
prlprl: Pearl dilution evident.
TO TO
to		 TOTO or TOto: Tobiano, a form of pinto patterning. Produces regular and distinct ovals or rounded patterns of white and color with a somewhat vertical orientation. White extends across the back, down the legs, but face and tail are usually dark.
toto: No tobiano pattern present.
O Also noted as Fr or FrO O
o		 OO or Oo: Overo or Frame Overo pattern - Pinto horse pattern that forms a solid frame around white spotting. White is usually horizontal in orientation with jagged edges, color crosses the back and legs, face is often white. Overo as an allele is different from overo as a registration since the registration also includes the splash overo and sabino alleles. Homozygous overo is associated with lethal white syndrome, characterized by an incomplete colon and the inability to defecate, which leads to death or humane euthanization within days of birth.
oo: No overo pattern present.
W W
w
WW: Lethal. Embryo reabsorbed or fetus dies en utero.


Ww: Horse has pink skin and white hair, brown or dark eyes. Hair coat is white from birth.
ww: Horse is fully pigmented.
G G
g		 GG or Gg: gray gene. Horse shows progressive silvering with age to white or flea-bitten, but is born a non-gray color. Pigment is always present in skin and eyes at all stages of silvering. Gray horses range from white to dark gray depending on age and the proportion of white hairs in the coat. Horses' coats gray in a manner similar to graying in human hair.
gg: Horse does not gray with aging.
Rn Rn
rn		 RnRn or Rnrn: roan pattern of white hair mixed in with base color. There quite likely is no lethal roan question.
rnrn: No roan pattern.
Sb Sb
sb		 Sabino - Assorted pinto or roan-like markings.
Sabino may be polygenic (a gene-complex rather than a single gene pair), caused by several different genes. Recognized by abundant white on the legs, belly spots or body spots that are can be flecked and roaned, chin spots, or white on the face extending past the eyes. Sabino is registered as overo by some registries, but is not the overo or frame overo allele. No risk of lethal white, though some "Fully expressed" sabinos may be completely white in coat color.
SbSb or Sbsb: Sabino markings.
sbsb: No sabino markings.
SB1:The only Sabino gene currently detected by DNA testing, however does not appear to be the gene that creates sabino coloring in Arabians or Clydesdales.
Lp Lp
lp		 Appaloosa or Leopard spotting gene. Produces coat spotting patterns, mottling over otherwise dark skin, striped hooves and white sclera around the eye.

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