Equine coat color genetics

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Horse Color Genetics

There are currently two horse color gentetic theories: Dr. Bowling's and Dr. Sponenberg's. These theories overlap, and are more similar than different. This is a combination of the two gene theories presented in Dr. Bowling’s clearer format.

To begin with, you need a basic understanding of heredity. If you need a quick lesson in genetics and heredity, Wikipedia’s article on alleles or this tutorial on inheritance can help you.

Note: for references to melanin (pigment or coloring): There are two chemically distinct types of melanin: the red–yellow phaeomelanin and the brown–black eumelanin. All coloration genes in mammalls affect either the production or final effect of these two chemicals.

Note 2: The terms Alleles and Modifiers are used interchangeably in this article.

Note 3: Socks, Star, Strip, and Snip genetics are not yet fully understood but probably multiple allele influenced.


Alleles and Effects

</TABLE>  

Genetic Formulas and Color Definitions

 


 
 

 
 
Alleles
Effect of Combined Pairs of Alleles 
W
W
w
The existence of a specific W gene is questioned by some.
WW: Lethal (Results in incomplete

colon and the inability to defecate. Probably from a gene near W or O but

not influencing the color directly.)

Ww: Horse typically lacks pigment in skin, hair and eyes and appears to be white. 

ww: Horse is fully pigmented.
G
G
g
GG or Gg: Horse shows progressive

slivering with age to white or flea-bitten, but is born a non-gray color. Pigment is always present in skin and eyes at all stages of silvering.

Gray colors range from white to dark gray as they do in human hair.
gg: Horse does not gray with aging. 
E
E
e
EE or Ee: Horse forms black pigment

in skin and hair. Black pigment in hair may be either in a points pattern

or uniformly distributed. 

ee: Horse has black pigment in skin, but red pigment in hair.Horse

will not appear red if white, gray, roaning, or dilution genes are present. 
E+ also noted as Ed
E+

 
 

<P class="MsoNormal">e+
E+E+or

E+e+ Dominant black, non-fading –Overrides the A or bay allele resulting

in all black horse

 

<P class="MsoNormal">e+e+ no effect
A
A
A
Agouti-Bay:

Acts on "E" to restrict eumelanin, or black pigment, to points.Has no effect

on "e" or red.
AA or Aa horse has black hair (E not E+), then that black hair shows only in points pttern. 
aa: If horse has E allele, then horse will be uniformly black..
C
C
CcrAlso noted as ‘c’		  
CCcrPalomino
CC Horse is fully pigmented. 


CCcr: Red pigment is diluted to yellow; black

pigment is unaffected
CcrCcrCremello CcrCcr
CcrCcr: Both

red and black pigments are diluted to pale cream. Skin and eye color are

also diluted.
D
 D  <P>d  DD

or Dd: Dun 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. 

<P>dd: Horse has undiluted coat color. 
TO
 TO  <P>to TOTO

or Toto: Produces regular and distinct ovals or round patterns of white and color that extend down over the neck and chest, giving the appearance of a shield. 

<P>toto: No tobiano pattern present. 
O Also noted as Fr or FrO 
O
o
OO

or Oo: Overo or Frame Overo pattern --color forms a frame around white patterning. Overo as an allele is different from overo as a registration since the registration also includes the splash and sabino alleles. Homozygous

associated with lethal white syndrome.
 
oo:No overo pattern present
Ch Ch


 


ch		 Champagne: A ra dilution gene that creates pumpkin-colored

freckled skin, amber or blue eyes, and gives a bronze cast to hair. The skin surrounding the eye must be pink with freckles. A champagne horse is born with a darker foal coat that lightens with maturity.
ChCh or Chch: champagne dilution evident (See Genetic Formulas Chart below.) 
 

<P>chch: no champagne dilution 


 
F F <P>f Effects visible on red or chestnut colors only.


FF or Ff:  Red points on ee horses 
 


ff:  flaxen points on ee horses 
P P


 


p		 Pangare (Mealy) The effects of this allele appear along

the underside of the horse, in the "soft" parts, or on the muzzle, behind the elbows, in the flanks, on the buttock, above or around the eyes, and along the belly.
PP or Pp:  Mealy or Pangare dilution of pigment 
 


pp:  no mealy looking lightening of pigment
Rn Rn


 


rn		 RnRn or Rnrn:  roan pattern of white hair mixed in

with base color. There is no lethal roan. (*See footnote.)
 


rnrn:  no roan pattern
Rb Rb 


rb


 		 Rabicano:  Partial roaning with ‘coon’ tail markings.

Thought to be a dominate gene by Sponenberg.
RbRb or Rbrb: rabicano markings 
 


rbrb: no rabicano traits
Sb Sb 

<P>sb


 		 Sabino Feathery Misty of Chincoteague like white markings.


Only paint marking pattern found in full blooded Arabians. Sabino may well be polygenic and causes abundant white on the legs, and then creeps up as belly spots and body spots that are can be flecked and roaned. Sabino is registered as overo but does not entail the overo or frame overo allele. No risk of lethal white. 
SbSb or Sbsb: sabino markings 
 


sbsb: no sabino marks
Spl Spl 


 

<P>spl


 		 Splash, Splashed White


Looks like reverse tobiano with white moving from the bottom of the horse towards the top. The horses head will look as if dunked in bucket of white paint. White coloring appears to move boldly and smoothly from bottom up. 
SplSpl or Splspl:  Splashed markings. Spash is registered as overo but has does not entail the overo or frame overo allele and is not associated with lethal white syndrome. 
 


splspl:  no splashed markings
Sty Sty <P>sty Sooty


 
StySty or Stysty:  black mixed into body coat. 
 


stysty:  no black mixed into coat
Z Z <P>z ZZ or Zz:   Silver dapple - dilutes eumelanin

or black pigment. Converts black to brown with white mane and tail or results in silver coloring.
 


zz:  no silver dapple
LpOp Appaloosa spotting gene. This gene is inferred and the

inference is disputed. Sponenberg is in favor of its existence. Others

maintain that it is a multiple allele trait.
Partial list of Genetic Formulas and Color Definitions
Chart based on Dr. Bowling’s Genetic Formulas
W  White 
G Gray
E, A, CC, dd, gg, ww, toto Bay or Brown 
E, aa, CC, dd, gg, ww, toto  Black
ee, aa, CC, dd, gg, ww, toto Red: Sorrel or Chestnut 
E, A, CCcr, dd, gg, ww, toto  Buckskin 
ee, CCcr, dd, gg, ww, toto Palomino
ee, CcrCcr Cremello
E, CcrCcr Perlino 
E, A, CC, D, gg, ww, toto Buckskin Dun
E, aa, CC, D, gg, ww, toto  Mouse Dun or Grulla
E,A,CC,D Dun, Zebra Dun, Bay Dun, Classic Dun 
ee, CC, D, gg, ww, toto  Red Dun 
gg, E, aa, CC, dd, RN  Black Roan (Blue Roan) 
gg, E, A, CC, dd, RN Bay Roan
gg, ee, CC, dd, RN  Red Roan
gg, E, A, CCcr, dd, RN  Buckskin Roan (Red Roan) 
gg, ee, CCcr, dd, RN  Palomino Roan (Red Roan)
gg, E, A, CC, D, RN  Buckskin Roan (Red Roan) 
gg, E, aa, CC, D, RN Mouse Dun Roan, Grulla Roan, or Blue Roan 
gg,ee, CC, D, RN  Red Dun Roan (Red Roan) 
gg, E, A, CC, dd, gg, ww, TO Bay Tobiano 
gg, ee, CC, D, gg, ww, TO  Red Dun Tobiano 
gg, Ch, ee, aa, CC, dd, gg, ww, toto Gold--looks like Palomino 
gg, Ch, E, A, CC, dd, gg, ww, toto  Amber
gg, Ch, E, aa, CC, dd, gg, ww, toto  Champagne 
gg, Ch, ee, CcrCcr  Ivory 
gg, E, aa, CC, dd, TO, Sb   Black Sabino-Tobiano (Tovero without lethal white.)
gg, E, aa, CC, dd, TO, O Black Tobiano-Overo (Tovero carrying lethal white.) 
ee, CCcr, dd, gg, ww, TO Palomino Tobiano Paint
gg, ee, aa, CC, dd, TO, Spl  Red Tobiano-Splash (Tovero without lethal white.) 


Lethal Roan Question

Hintz, H.F. and VanVleck, L.D., published 1979. Lethal Dominant Roan in Horses. Journal of Heredity 70:145-146. This study, based on percentages of roan foals thrown by roan parents, popularized the idea of Lethal Roan Syndrome. The study did not include direct genetic analysis and assumed fetus absorption preventing birth.

A recent genetic study of roans by Dr. Bowling (See http://www.hancockhorses.com/article-roanQHNews.pdf) refuted Hintz and VanVleck’s inferences. Using genetic analysis, Dr. Bowling found several homozygous roans and no evidence of a Lethal Roan Syndrome.


Sources and External Links


http://www.dreamviewfarm.com/genetics.html Main base for this arcticle. Used with author's permission.

http://www.mustangs4us.com/

http://www.vgl.ucdavis.edu/~lvmillon/ Ann T. Bowling, PhD Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis, California 95616-8744

http://members.aol.com/MFTHorses/sponenbg.htm D. Phillip Sponenberg, DVM, PhD. Virginia-Maryland Regional College of Veterinary Medicine, Virginia Tech, Blacksburg, VA 24061

http://www.grullablue.com

http://www.hancockhorses.com/article-roan.html

http://www.hancockhorses.com/article-roanQHNews.pdf

http://www.equinecolor.com/ Provides clear explanations—a good source for the beginner. Does contain info on ‘possible lethal roan’.

http://www.ichregistry.com/identification.htm

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