Genetics of Equine
Colors, plus Directory of online EQUINE COLOR Links on the Internet
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*Apache
Rose
base coat colors:
red
black
CAPITAL letter = dominant, or expressed
small letter = recessive, or not expressed
E allows black hair. (entire coat or just
points)
e does not allow black hair. ee
= red (chestnut / sorrel)
A (agouti gene) confines any black hair to points
= bay horse
a no restriction in distribution of black
hair = black horse
If a horse has black hair - either black or black points (bay), then the
animal possesses an allele of the E gene which contains the instructions
for placing black pigment in hair. Geneticists symbolize this allele of the
E gene E. The alternative allele to E is e. Allele e
allows black pigment in the skin but not in the hair. The pigment conditioned
by the e allele makes the hair appear red. If an animal has no black
pigmented hair, it has the genetic formula ee. Basically, an ee
animal will be some shade of red ranging from light sorrel to dark chestnut.
(The genetics of these variations has not been defined.)
The gene that controls the distribution pattern of black hair is known as
A. The allele A in combination with E will confine the
black hair to the points to produce a bay. Various shades of bay from dark
bay or brown through mahogany bay, blood bay to copper bay and light bay
exist. (The genetics of these variations has not been defined.) Any bay horse
will include A and E in its genetic formula. The alternative
allele a does not restrict the distribution of black hair and thus
in the presence of the allele E of the E gene a uniformly black horse
is produced. In most breeds of horses, the a allele is rare, so black
horses are fairly infrequent. Many black horses will sun-fade, especially
around the muzzle and flanks and such animals may be called brown. The term
brown can be used for several genetic combinations (various reds, bays and
dark bays, as well as some blacks). It was thought in the past that seal
browns were just black horses with the Pangaré (mealy) gene, but in
2001 when the "a" allele was isolated and researched in France, none of the
seal browns tested were "aa" -- showing that seal brown IS caused by an Agouti
allele, and not by Pangaré. (most of this
info is taken from UC Davis horse color genetics site)
dilution genes:
on a horse's body coat color:
dun ~ modifies (lightens) red and black (not necessarily
black points)
creme ~ modifies red, incomplete dominant (2 genes modify
more than 1 gene)
champagne ~ modifies red and black (not necessarily
black points)
silver dapple ~ modifies black
tables of genetic
color combinations:
black, red, bay
(agouti)
+AA agouti
+Aa agouti
+aa (no agouti)
EE =
homozygous
black
bay
bay
black
Ee =
heterozygous
black
bay
bay
black
ee =
no black
sorrel
sorrel
sorrel
sorrel
dilutes on black,
red, bay
heteroz-creme
homoz-creme
dun
champagne
silver dapple*
sorrel
palomino
cremello
red dun
gold champagne
silver (mimic) sorrel
black
smoky blk
smoky creme
grullo / grulla
amber champagne
silver dapple
bay
buckskin
perlino
dun
classic champagne
silver bay
*if two horses appearing to be sorrels, produce a bay foal;
then all should be tested - some SD's are mistaken for chestnut
but are really a silver bay and the testing (Ee Aa) will prove it.
Observed
Effect of Alleles in Homozygous and Heterozygous Condition
black
E
E, e
EE: horse has ability to form black pigment
in skin and hair. black pigment in hair may be either in a points pattern
or distributed overall.
Ee: same as EE.
ee: horse has black pigment in skin, but hair
pigment appears red.
bay (Agouti)
A
A, a
AA: if horse has black hair (E), then that
black hair is in points pattern. A has no effect on red (ee) pigment.
Aa: same as AA.
aa: if horse has black hair (E), then
that black hair is uniformly distributed over body and points. A has no effect
on red (ee) pigment.
creme
C
C, Ccr
CC: horse is fully pigmented.
CCcr: red pigment is diluted to yellow;
black pigment is unaffected.
CcrCcr: both red and black pigments are
diluted to pale cream. skin and eye color are also diluted.
dun
D
D, d
DD: 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: same as DD.
dd: horse has undiluted coat color.
GG: horse shows progressive silvering with
age to white or flea-bitten, but is born any non-gray color. pigment is always
present in skin and eyes at all stages of silvering.
Gg: same as GG.
gg: horse does not show progressive silvering
with age.
tobiano
TO
TO, to
TOTO: horse is characterized by white spotting
pattern known as tobiano. legs are usually white.
TOto: same as TOTO.
toto: no tobiano pattern present.
white
W
W, w
WW: lethal
Ww: frame overo
(not from UC Davis site, this is our simplified
clarification)
ww: horse is fully pigmented.
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