Horse Coat Color Genetics

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Horse Coat Color Genetics
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Coat Colors- BackgroundColors

• Due to pigment in hair
• Two major pigments all colors
• Eumelanin black or slate blue
• Either on or off (all or none)
• Pheomelanin reddish brown to yellow
• Most have both

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Coat Colors- BackgroundColors

• Melanocytes produce either pheomelanin or
  eumelanin
• Melanocyte stimulating hormone (MSH)
• Cell surface receptor for MSH
• If activated eumelanin (black)
• If not activated/blocked pheomelanin (chestnut)

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Coat Colors- BackgroundColors

• Background colors are independent of any white
  marking
• White hair is not a true color
• White hair is absence of pigment
• Background color is blocked by white

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Coat Colors- Points

• Points- main, tail, lower legs and ear rims
• Black points
• Non-black points
• Red
• Cream
• Brown

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White Gene

• WW embryonic lethal (dominant)
• ww all non-white horses
• Ww masks all other coat color genes
• Skin is pink
• Eyes are brown or blue
• Hair is white

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Gray Gene

• gg all non-gray, non-white horses
• GG or Gg dominant
• Born dark and turn progressively gray
• Progressive silvering with age
• Increase in white hairs
• Skin is black

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Gray Gene
Genotype wwG_
SJ Farms
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Gray Gene
Genotype wwG_
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Coat Colors- basic darks

• Bay, chestnut and black - most horses
• Most other coats start with one of these
• Bay black points on reddish brown body
• Chestnut shade of red with non-black points
• Black black body and points
• Rare in general
• Common in some breeds (Percheron, Friesian,
  Shire)

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Coat Colors- basic darks

• Extension dominant
• MSH (melanocyte-stimulating hormone) receptor
  activated
• EE or Ee black pigment in hair (black or bay)
• ee inactive MSH receptors (chestnut)
• Agouti dominant
• controls distribution of black pigment
• Protein blocks MSH receptor
• AA or Aa restricts black to points (bay)
• aa recessive allele black all over (black)

Result of two genes Agouti and Extension
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Coat Colors- basic darks
Result of two genes Agouti and Extension

• Agouti dominant
• controls distribution of black pigment
• Agouti protein blocks melanocyte receptor for
  melanocyte-stimulating hormone
• Cant be stimulated
• Only produce pheomelanin (chestnut)
• aa genotype
• No blockage which allows stimulation
• Produce eumelanin (black)
• Regional distribution is genetic

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Coat Colors- basic darks
Dilution of Pigment

• Production of pigments
• Overlaping pathways
• Mutations not well characterized
• Packaging of pigments
• Produced in melanocytes
• Packaged in melanosomes
• Melanosomes moved to hair and skin
• Amount of pigment per melanosome
• Distribution of melanosomes

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Extension (Black) Gene

• ee red or brown hair
• EE or Ee hair is black
• Skin is black

Genotype
Not white ww
Not grey gg
wwggE_
black EE or E_
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Extension (Black) Gene
Not white ww
Not grey gg
black EE or E_
SJ Farms
Genotype wwggE_
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Extension (Black) Gene
gg
ww
E_
Mare
Not white ww
Not grey gg
Black EE or E_
ww
gg
ee
Foal
Not white ww
Not grey gg
Not black ee
Since baby is ee -
Mare wwggEe Foal - wwggee
Mom must be Ee
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Extension (Black) Gene - ee
Mare wwggee Foal - wwggee
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Agouti Gene A - Points

• AA or Aa black hair confined to points
• Mane, tail and legs
• Bay horse
• aa no restriction
• of black color
• Dark horse

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Agouti Gene A - Points
Bay Mare wwggE_A_
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Agouti Gene A - Points
Bay Mares wwggE_A_
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Coat Colors- Shade differences

• Variations of light and dark
• Usually seen on chestnuts
• Complex, multifactorial genetics
• Different names for different shades

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Coat Colors- Shade differences
Liver chestnut
Red chestnut
Golden chestnut
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Coat Colors- Shade differences
Golden bay
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Coat Colors- Pigment Dilution

• Pale horse colors derived from bay, chestnut and
  black
• Two major types
• Cream-related colors
• Dun

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Gene C Pigment Dilution

• CC fully pigmented horse
• CCcr
• Black pigment not affected
• Red pigment diluted to yellow
• Buckskin yellow with black points
• Palomino yellow horse with light mane and tail
• CcrCcr completely dilutes ANY color
• Cremello or albino

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Gene C Pigment Dilution

• CCcr
• Black horse w/ CCcr black
• Chestnut w/ CCcr palomino
• Bay w/ CCcr buckskin

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Gene C Pigment Dilution

• Buckskin yellow with black points
• Bay horse with CCcr
• wwggA-E-CCcr

UC Davis
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Gene C Pigment Dilution

• Palomino yellow horse with light mane and tail
• Red horse with CCcr
• wwggeeCCcr

UC Davis
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Gene C Pigment Dilution

• CcrCcr completely dilutes ANY color
• - cream horse
• - difficult to distinquish from white
• - cremello or albino

UC Davis
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Coat Colors- Pigment Dilution

• Dun or linebacked dun
• Primitive marks
• Darker marking
• Dorsal stripe down back
• Stripes on legs
• Withers stripe

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Gene Dn Dun Pattern

• DnDn and Dndn dun dilution pattern
• Dark points, dorsal and shoulder stripe and leg
  barring
• Both Black and red pigment affected
• Does not affect color of points
• Red diluted to pinkish or yellowish
• Black diluted to gray
• dndn fully pigmented

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Gene Dn Dun Pattern

• Zebra dun
• Black points
• Black or dark primitive marks
• Tan bodies
• Heads somewhat darker

• Grullo or blue dun
• Darker than zebra
• Black points
• Black primitive marks
• Beige to slate bodies
• Black or dark heads

• Red dun
• Brownish points
• Dark primitive marks
• Paler brown bodies
• Heads somewhat darker

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Gene Dn Dun Pattern

• Dn -
• Black grey or beige (grullo)
• Bay red to tan (zebra dun)
• Chestnut light red (red dun)
• Points usually unaffected
• Primitive marks visible
• dndn
• Fully pigmented

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Gene Dn Dun Pattern
Zebra Dun
SJ Farms
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Gene Dn Dun Pattern
Zebra dun
Grullo
Red dun
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WhiteSpotting Patterns
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Roan Pattern

• Mixture of white and dark hairs
• Variable extent of white
• Usual pattern
• body whitish
• Legs and head dark
• Usually present at birth but
• Not progressive like Gray

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Roan Pattern

• Rn_ is dominant to rn rn
• Combines with any base coat color
• Black Rn blue roan
• Bay Rn red roan
• Chestnut Rn Strawberry/purple roan

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Roan Pattern
Strawberry/purple roan
UC Davis
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Roan Pattern
Red roan
blue roan
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Patterns of White

• Pattern on base color
• Each pattern is independent
• Complex
• Paints w/ at least 4 genes
• Confusing overlapping names

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Tobiano Spotting

• White hair with underlying pink skin
• Any coat color
• Stable pattern
• White hooves
• White lower legs
• Asymmetrical
• Body spotting which crosses midline
• Sharply defined boarders
• TOTO and TOto

Red tobiano
UC Davis
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Tobiano Spotting
Chestnut tobiano
Black tobiano
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Leopard/Appaloosa Complex

• Several patterns included
• Any coat color
• Symmetrical
• Sparse mane and tail hair
• Variations in pigment concentration
• Usually also have
• striped hooves
• Mottled skin
• Prominent white sclera

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Leopard/Appaloosa Complex

• LpLp single dominant
• Many modifiers
• Blanket pattern
• White croup and hips
• Some with dark spots
• Leopard pattern
• White horse with dark spots
• Spots are base color
• Snowflake pattern
• Small white spots overall

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Leopard/Appaloosa Complex
SJ Farms
Leopard
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Leopard/Appaloosa Complex
UC Davis
Black
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Leopard/Appaloosa Complex
Leopard
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Identify these Genotypes
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Example 1
SJ Farms
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Example 1
Start by asking the following
SJ Farms

• Is the horse coat white?
• If yes, is skin pink?
• Yesgenotype is Ww
• No genotype is ww

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Example 1
Continue asking the following
SJ Farms

• 2) Is the horse base coat white/grey/greying?
• If yes, is skin black?
• Yesgenotype is G-
• No genotype is gg

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Example 1
Continue asking the following
SJ Farms

• 3) Is the horse base coat black or Chestnut?
• Black.genotype is E-
• Chestnut.genotype is ee

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Example 1
Continue asking the following
SJ Farms

• 4) Is the horse base coat bay?
• Bay.genotype is A-
• Solid.genotype is aa

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Example 2
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Example 2
Start by asking the following

• Is the horse coat white?
• If yes, is skin pink?
• Yesgenotype is Ww
• No genotype is ww

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Example 2
Continue asking the following

• 2) Is the horse base coat white/grey/greying?
• If yes, is skin black?
• Yesgenotype is G-
• No genotype is gg

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Example 2
Continue asking the following

• 3) Is the horse base coat black or Chestnut?
• Black.genotype is E-
• Chestnut.genotype is ee

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Example 2
Continue asking the following

• 4) Is the horse base coat bay?
• Bay.genotype is A-
• Solid.genotype is aa

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Example 3
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Example 3
Start by asking the following

• Is the horse coat white?
• If yes, is skin pink?
• Yesgenotype is Ww
• No genotype is ww

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Example 3
Continue asking the following

• 2) Is the horse base coat white/grey/greying?
• If yes, is skin black?
• Yesgenotype is G-
• No genotype is gg

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Example 3
Continue asking the following

• 3) Is the horse base coat black or Chestnut?
• Black.genotype is E-
• Chestnut.genotype is ee

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Example 3
Continue asking the following

• 4) Is the horse base coat bay?
• Bay.genotype is A-
• Solid.genotype is aa

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SJ Farms
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UC Davis
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SJ Farms
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SJ Farms
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Shamrock Farm
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References

• Bowling, A. UC Davis web page http//www.vgl.ucda
  vis.edu/lvmillion/coatcolor/coatclr3.html
• Sponenberg, DP. Equine Color Genetics. 2nd ed.
  Blackwell Pub. Iowa.2003.