Equine Coat Color Genetics Jenny Ingwerson

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Equine Coat Color GeneticsJenny Ingwerson
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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

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Basic Principles

• 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

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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)
• Pheomelanin (red or yellow)

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Coat Color Extension E e

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

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Coat Color - AGOUTI A a

• Controls the distribution pattern of black hair
• Restricts dark pigment to points with E
• Only effects eumelanin (black and brown
  pigmentation)
• A dominant to a
• E_A_ bay or brown
• E_aa black
• eeA_ or eeaa chestnut

Chestnuts like any recessive, will always
breed true chestnut x chestnut chestnut
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Coat Color Dilution Genes

• 2 main loci responsible - C and D
• C locus - Palomino dilution
• Ccr gene is partially dominant
• Ccr - red pigmentation is diluted to yellow
• Dilutes only pheomelanin, so black horses are
  unaffected
• For a chestnut horse
• CC chestnut
• C Ccr palomino
• Ccr Ccr cremello
• For a bay horse
• CC bay
• C Ccr buckskin
• Ccr Ccr perlino

Cremello
Sire of cremello
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Coat Color

• DILUTION GENES (cont.)
• C locus - Palomino dilution
• This is why palominos do not breed true!
  CCcr x CCcr
• 25CC 50 CCcr 25 Ccr Ccr

Palomino or buckskin
Cremllo or Perlino
Not diluted
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Coat Color

• D locus - dominant dilution
• Dun dilution
• D dominant to d
• 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
• Black base coat
• D_ grulla
• dd black
• Bay base coat
• D_ dun
• dd bay

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Coat Color

• D locus
• Chestnut base coat
• D_ red dun
• dd chestnut
• Duns usually have a dorsal stripe, buckskins do
  not

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White W w

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

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Coat Color Gray G g

• G_ gray
• gg normal color
• Born colored
• Hairs progressively replaced by white hairs
• Must have at least one gray parent
• Horses continue to gray with age

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Coat Color Roan Rn rn

• Rn Rn lethal theory
• Rn rn roan
• rn rn normal color
• Roan horses are born roan - the number of white
  hairs does not increase
• Must have at least one roan parent

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Coat Color White Patterns

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

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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.