Transcript Horse Color & Genetics - NAAE Communities of Practice

Horse Color &
Genetics
Reference:
http://www.equinecolor.com
Evans, W., The Horse,2ed. 1990 “Genetics:
Color inheritance, Parentage testing,
Genetic Lethals”, pp.472-536
Black phenotype
Black bodies
 Black points
 Black horses
without any
brown or red
hairs

Black genotype
1.
Genetic Information
a. Black pigment = Eumelanin (yoo-MEL-a-nin)
b. Black is one of the base colors for horses, the other is red
(Chestnut).
•
•
•
c.
Black at the Extension locus is symbolized by "E", since it is
dominant.
•
d.
e.
f.
g.
All horses will have a black or red base color.
The control for Black is located at the Extension locus and is
dominant at that locus.
Black horses are not capable of producing Bay foals unless the
mate is a Bay or a Chestnut masking Agouti.
Chestnut is also located at the Extension but it is recessive so
it's symbolized by "e".
EE means the horse is genetically (homozygous) and
physically Black*
Ee means the horse is genetically (heterozygous) and
physically Black*
ee means the horse is genetically and physically Chestnut*
*These horses are physically Black or Chestnut when there
are no dilution or modifying genes present.
Chestnut Phenotype
Red bodies
 Red points

– Flaxen
• Light mane tail

Sorrel
– Accepted color in
AQHA
Chestnut (red) Genotype
1.
Genetic control of Chestnut is fairly simple to
understand.
a.
b.
Base coat color
The recessive gene (labeled "e") resides at the
Extension locus.
•
•
•
2.
EE =Black
Ee =Physically black
ee = Chestnut
Point color on Chestnuts doesn't seem to be
controlled by a single gene.
a.
Flaxen is thought to be caused by a recessive gene
and is unique in that it only affects red pigment.
Gray Phenotype




More accurately Grey is
a modifier
Ongoing process of
depigmentation of the
colored hairs
Grey slowly removes the
pigment from the base
color
Black base coat with
white diluting hairs
throughout the body
Gray Genotype
Grey has the unique ability to mask
everything including any Pinto or Appaloosa
patterns.
No color is safe when Grey is present, as
all horses that carry the Graying gene will
end up a shade of grey or white.
1.
2.
•
For this reason some breeders do not like to
have mares or stallions in their breeding herd.
Gray is dominant
3.
•
•
•
GG = Gray
Gg = physically grey
gg = no dilution (base coat appears)

Red body, ranging from
light to dark
 Black legs from the hoof
to the knee and hock
– Sometimes extending
above the knee and
hock.

The mane and tail will
also be black.
– Bay horses generally
have black ear tips also.

"Wild" Bay
– the black points are
restricted lower on the
legs, to varying degrees.
Bay Phenotype
Bay Genotype

Bay
– Black horse with a restrictor or modifying type
gene.
• This locus is called Agouti.
– Agouti restricts the black pigment to the "points" of
the horse, or the lower legs, mane and tail.

Agouti locus
–
–
–
–
A+ = wild bay
A = Bay
at = seal brown (black with brown points)
a = black
Dun
Bay
Cccr
Buckskin
Dun or
DD
Dd
AA
Aat
Perlino
ccrccr
DD
Brown Grulla
DD
Black
Dd
aa
Cccr
Aa
ccrccr
“Black”
EE
Ee
a ta t
a ta
Seal Brown
Cccr
Diluted seal
brown
Grulla
ccrccr
Dd
No
agouti
affect
DD
Red Dun
Chestnut Dd
Cccr
Palomino
Cremello
ccrccr
Bay base color
 Dun dilutes

– Bay base color
– Dun dilution
Dun Phenotype
• Black
• Red pigment
• Dun dilution causes
different types of
Dun

Primitive markings
– Dorsal stripe
– It may or may not
have
• Zebra stripes on legs
• Transverse stripe over
wither
Dun Genotype

Dilution gene
 Dominant dilution
 Affects Black, Chestnut, and Bay
 DD, Dd = Dun
 dd = no dilution
Grulla Phenotype

Black Dun
 Primitive markings
– Dorsal stripe
– Zebra stripes on legs
– Transverse wither

Mousey gray
Grulla
Rare gene
 No Agouti gene dilution

– Therefore the Black base coat appears
DD, Dd = Black Dun
 dd = no dilution

Palomino
Phenotype
1.
Golden yellow
 Ideal
 New United States
gold coin
 Shades light to dark
 Born very light to
white
 Pink skin at time but
will darken
 Brown to light amber
eyes
 It may take several
years for a horse to
turn golden
2.
White mane and tail
 85% white
 No more than 15%
black/brown hairs
Palomino Genotype

Cream dilution
– Present on the albino locus (not albino)
– Appears in conjunction with Agouti
– Recessive gene--somewhat
– CC = Base coat will appear
• Black, Chestnut, or Bay
– Cccr = Cream dilution
• Palomino
– Base coat = chestnut with dilution
Buckskin Phenotype

Light bay
 Gold to yellow coat
 Black points
 No dorsal stripe
Buckskin Genotype

Cream dilution
– Present on the albino locus (not albino)
– Appears in conjunction with Agouti
– Recessive gene--somewhat
– CC = Base coat will appear
• Black, Chestnut, or Bay
– Cccr = Cream dilution
• Buckskin
– Base coat = bay with dilution
Perlino Phenotype

Light or pink skin
 White or cream
colored hair coat
 Mane, tail and legs
slightly darker than
the body
 Blue eyes
Perlino Genotype

Cream dilution
– Present on the albino locus (not albino)
– Appears in conjunction with Agouti
– Recessive gene--somewhat
– CC = Base coat will appear
• Black, Chestnut, or Bay
– Cccr = Cream dilution
• Palomino or Buckskin
– ccrccr = Highest dilution
• Bay base coat and dilution = Perlino
Cremello Phenotype

Light or pink skin
 White or cream
colored hair coat
 Mane, tail and legs
crème
 Blue eyes
Cremello Genotype

Cream dilution
–
–
–
–
Present on the albino locus (not albino)
Appears in conjunction with Agouti
Recessive gene--somewhat
CC = Base coat will appear
• Black, Chestnut, or Bay
– Cccr = Cream dilution
• Palomino or Buckskin
– ccrccr = Highest dilution
• Chestnut base coat and dilution = Cremello
White trait

Causes patterns
–
–
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–

Appaloosa
Overo
Tobiano
Lethal gene?
Modifying Gene
–
–
–
–
Masks color
WW = birth terminated
Ww = white hair coat, pink skin
ww = No white, ie. Color expressed
Appaloosa Phenotype/Genotype

Pattern
–
–
–
–
–
–

Leopard
Blanket
Snowcap
Snowflake
Varnish roan
Frost
Mottled skin
– Grey, pink patterned skin

Striped hooves
 White sclera around the
eye
 WapWap = Leopard
 Wapwap = other pattern
 wapwap = no pattern
Overo Phenotype/Genotype

“Frame”
– White framed by color
• Wild irregular pattern
• Less likely symmetrical
– Typically does not cross
the topline
– Crop-outs occur

Recessive gene
– oeoe = Lethal Gene
– oo, ooe = patterned horse
– Ooe, Oo = non Patterned
horse, but carrier
– OO = no pattern
Tobiano Phenotype/Genotype

Vertical pattern crossing
the topline
– White between the ears
and tail
– Head usually solid color
– Round patterns

Dominant Gene
– TT, Tt = Tobiano
– tt = normal expression
(color)
– Both parents should be
Tobiano to get a Tobiano
Lethal Genes
1.
Homozygous
Dominant White
Gene
 Result of
heterozygous cross
 WW = not born
 Ww = white horse
 ww = color
expressed
1.
OLWS

Overo Lethal White
Syndrome
–
–
Carried full term
Born totally white
•

These foals have an
incomplete lower colon
•
•
•
•


some may have a tiny
spot or two of color.
Foals cannot defecate
Die of colic shortly after
birth
A positive test of the gene
Recommends to
euthanize
Frame gene
Recessive gene
– oeoe = Lethal Gene
– oo, ooe = patterned horse
– Ooe, Oo = non Patterned
horse, but carrier
– OO = no pattern
Roan

Pattern caused
– White hairs mixing
with colored hairs

Non-progressive color
– Visible by a few months
of age
– May become darker
– Seasonal change




Head, legs, mane and
tail solid color
RnRn =Lethal (before
birth)
Rnrn = Roan
rnrn = no expression