Download Coat color genetics 06

Equine Coat Color Genetics
Jenny Ingwerson
Basic Principles
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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
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When paired alleles are not identical, the horse
is heterozygous at that locus
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When paired alleles are identical, the horse is
homozygous at that locus
Qualitative Coat Color
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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)
Coat Color – Extension: E e
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E
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e
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Black pigmented horses
Either black as points or
black as entire coat color
 blacks, browns and bays,
buckskins, duns, etc
Black pigment in skin but not
in hair
Hair appears red
 chestnuts, red duns,
palominos, etc.
E dominant to e
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EE or Ee = black or bay (or
brown)
ee = chestnut
Coat Color - AGOUTI: A a
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Controls the distribution pattern of black hair
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Restricts dark pigment to points with E
Only effects eumelanin (black and brown
pigmentation)
A dominant to a
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E_A_ = bay or brown
E_aa = black
eeA_ or eeaa = chestnut
**Chestnuts
like any recessive, will always
breed true
chestnut x chestnut = chestnut
Coat Color – Dilution Genes
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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:
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CC : chestnut
C Ccr : palomino
Ccr Ccr : cremello
For a bay horse:
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CC : bay
C Ccr : buckskin
Ccr Ccr: perlino
Sire of cremello
Cremello
Coat Color
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DILUTION GENES (cont.)
C locus - “Palomino dilution”
This is why palominos do not breed true!
CCcr x CCcr
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25%CC
Not diluted
50% CCcr
Palomino or buckskin
25% Ccr Ccr
Cremllo or Perlino
Coat Color
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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
Coat Color
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D locus
 Chestnut base coat:
 D_ = red dun
 dd = chestnut
 Duns usually have a
dorsal stripe, buckskins
do not
White – W w
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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
Coat Color – Gray G g
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G_ = gray
gg = normal color
Born colored
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Hairs progressively
replaced by white hairs
Must have at least one
gray parent
Horses continue to gray
with age
Coat Color – Roan Rn rn
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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
Coat Color – White Patterns
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Tobiano (T locus)
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Overo (frame)
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T_ = spotted
tt = nonspotted
Any base color can be spotted
Can test for allele
Was thought to be recessive, but
now determined dominant
Appaloosa - unclear inheritance
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Markings - probably due to many
genes
Rules
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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.