Equine Coat Color Genetics Jenny Ingwerson

Basic Principles  32 pairs of chromosomes  Genes control expression of traits and are located along chromosome  Each parent contributes 50% of genetic makeup  Pairs of genes at the same physical location (locus) on a chromosome are called alleles

Basic Principles When paired alleles are not identical, the horse is heterozygous at that locus When paired alleles are not identical, the horse is heterozygous at that locus When paired alleles are identical, the horse is homozygous at that locus When paired alleles are identical, the horse is homozygous at that locus

Qualitative Coat Color  More than 10 loci involved  Many epistatic effects  At any one locus, effects are generally due to dominance  Two types of skin pigmentation Eumelanin (black or brown) Eumelanin (black or brown) Pheomelanin (red or yellow) Pheomelanin (red or yellow)

Coat Color – Extension: E e  E Black pigmented horses Black pigmented horses Either black as points or black as entire coat color Either black as points or black as entire coat color blacks, browns and bays, buckskins, duns, etc blacks, browns and bays, buckskins, duns, etc  e Black pigment in skin but not in hair Black pigment in skin but not in hair Hair appears red Hair appears red chestnuts, red duns, palominos, etc. chestnuts, red duns, palominos, etc. E dominant to e E dominant to e EE or Ee = black or bay (or brown) EE or Ee = black or bay (or brown) ee = chestnut ee = chestnut

Coat Color - AGOUTI: A a  Controls the distribution pattern of black hair Restricts dark pigment to points with E Restricts dark pigment to points with E Only effects eumelanin (black and brown pigmentation) Only effects eumelanin (black and brown pigmentation) A dominant to a A dominant to a E_A_ = bay or brown E_A_ = bay or brown E_aa = black E_aa = black eeA_ or eeaa = chestnut eeA_ or eeaa = chestnut **Chestnuts like any recessive, will always breed true like any recessive, will always breed true chestnut x chestnut = chestnut

Coat Color – Dilution Genes  2 main loci responsible - C and D  C locus - “Palomino dilution”  C cr gene is partially dominant C cr - red pigmentation is diluted to yellow C cr - red pigmentation is diluted to yellow Dilutes only pheomelanin, so black horses are unaffected Dilutes only pheomelanin, so black horses are unaffected For a chestnut horse: For a chestnut horse: CC : chestnut CC : chestnut C C cr : palomino C C cr : palomino C cr C cr : cremello C cr C cr : cremello For a bay horse: For a bay horse: CC : bay CC : bay C C cr : buckskin C C cr : buckskin C cr C cr: perlino C cr C cr: perlino Cremello Sire of cremello

Coat Color  DILUTION GENES (cont.)  C locus - “Palomino dilution”  This is why palominos do not breed true! CC cr x CC cr 25%CC 50% CC cr 25% C cr C cr 25%CC 50% CC cr 25% C cr C cr Palomino or buckskinCremllo or PerlinoNot diluted

Coat Color D locus - “dominant dilution” D locus - “dominant dilution” Dun dilution Dun dilution D dominant to d D dominant to d Dilutes both black and red pigment on body but not points of horse Dilutes both black and red pigment on body but not points of horse Common to see dark points, dorsal stripe, shoulder stripe and leg barring Common to see dark points, dorsal stripe, shoulder stripe and leg barring Black base coat: Black base coat: D_ = grulla D_ = grulla dd = black dd = black Bay base coat: Bay base coat: D_ = dun D_ = dun dd = bay dd = bay

Coat Color  D locus Chestnut base coat: Chestnut base coat: D_ = red dun D_ = red dun dd = chestnut dd = chestnut Duns usually have a dorsal stripe, buckskins do not Duns usually have a dorsal stripe, buckskins do not

White – W w Inability to form pigment in skin & hair Inability to form pigment in skin & hair Epistatic to all other colors Epistatic to all other colors True albinos have a white coat, mane, and tail, with pink skin and pink eyes True albinos have a white coat, mane, and tail, with pink skin and pink eyesalbino WW = lethal (in utero) WW = lethal (in utero) Ww = white Ww = white ww = normal color ww = normal color All white horse are born white and have pink skin All white horse are born white and have pink skin Eyes can either be dark or blue Eyes can either be dark or blue

Coat Color – Gray G g G_ = gray G_ = gray gg = normal color gg = normal color Born colored Born colored Hairs progressively replaced by white hairs Hairs progressively replaced by white hairs Must have at least one gray parent Must have at least one gray parent Horses continue to gray with age Horses continue to gray with age

Coat Color – Roan Rn rn Rn Rn = “lethal theory” Rn Rn = “lethal theory” Rn rn = roan Rn rn = roan rn rn = normal color rn rn = normal color Roan horses are born roan - the number of white hairs does not increase Roan horses are born roan - the number of white hairs does not increase Must have at least one roan parent Must have at least one roan parent

Coat Color – White Patterns Tobiano (T locus) Tobiano (T locus) T_ = spotted T_ = spotted tt = nonspotted tt = nonspotted Any base color can be spotted Any base color can be spotted Can test for allele Can test for allele Overo (frame) Overo (frame) Was thought to be recessive, but now determined dominant Was thought to be recessive, but now determined dominant Appaloosa - unclear inheritance Appaloosa - unclear inheritance Markings - probably due to many genes Markings - probably due to many genes

Rules It usually takes at least one light-colored parent to produce a light-colored foal. Chestnut and sorrel, when mated to one another, can produce only more chestnuts and sorrels. Bay mated to bay, black or chestnut/sorrel can produce bay, chestnut, sorrel, and, rarely, black. Black mated to black produces black (or, rarely, chestnut or sorrel). Black mated to bay will usually produce a bay, fairly commonly produces chestnut or sorrel, and only rarely produces black. Black mated to chestnut will usually produce bay, but also chestnut or sorrel, and, rarely, black. Color prediction is never 100 percent accurate.