Genetics Notation

Capital Letter = Dominant, expressed, trait is genetically "switched on"
Small letter= not expressed, trait is not "switched on"; or Recessive gene

I have listed below common genetic notation used by two of the most widely-accepted sources - Dr. Phil Sponenberg and Dr. Ann Bowling. In some cases, different notation is used, but if you look carefully, you will find that they are saying the same thing.

Remember that genetic notation is based on theories, which are used to explain Real World experiences.   It is perfectly okay for one geneticist to use one system of genetic notation and another to use a different system, since it is all theoretical anyway. Only a few color genes have been definitively identified. These include red, black, Tobiano, and Frame (Overo).

"Locus"  - meaning "place" can be a confusing term to the beginner. It refers to the placement of a certain factor on a DNA string.  I prefer to use the term "genetic modifier," which is also used by Dr. Ann Bowling and the UC Davis biology dept.

Color genetics are the same for all horses, regardless of breed or ancestry.

Since this is a Mustang website, I use pictures of wild, or formerly-wild horses wherever possible.
Gene Name & What it doesResult
AAgouti (Bay Modifier): Acts on "E" to restrict eumelanin  to points; No effect on "e" or redBay
CNon-diluteFull Color
CcrCreme: Dilutes phaeomelanin markedly, eumelanin a little

A single Ccr on RED = Palomino

A single Ccr on BLACK = Smoky Black

A single Ccr on BAY=Buckskin

Double Ccr dilutes the single creme colors even further:
Double Ccr on Red = Cremello

Double Ccr on Black = Smokey Cream

Double Ccr on BAY = Perlino
Photo: Andi Harmon; perlino mustang adopted by Greg Schultz

ChChampagne: A dilution gene that creates pumpkin-colored freckled skin, amber eyes, and unique bronze cast to hair coat Champagne
Champagne gene on Red =Gold Champagne on Bay = Amber
Champagne on Black =Classic
Champagne + Creme =  Ivory
DDun dilution - dilutes both eumelanin and phaeomelaninDun on Red = Red Dun
Dun on Bay = Dun, Zebra Dun, Bay Dun, Classic Dun
Dun on Black = Grulla/o
dNon-diluteFull Color
Ed, E+Dominant black, epistatic to A locusBlack
EDominant form of "Extension" locus; Allows either eumelanin (black pigment) or pheomelanin (red pigment) * (normal notation)Black, unless other gene, such as A modifies

Ranger from Coyote Lakes and his adopter, Karen Blackwood
Recessive form of "extension" locus; Allows Phaeomelanin (red pigment)only;  epistatic to A locusRed (chestnut, sorrel)
FRed points on ee horsesTostado or alazan
fFlaxen points on ee horses

(This is Sponenberg notation; not everyone recognizes flaxen)

Frame Overo

"Fr" is not the commonly accepted genetic symbol for frame overo. "O" is used in all scientific publications. Sponenberg uses the Fr symbol, but most others use Oo.


Frame Overo

Also: Overo Lethal White Syndrome


Grey - gradually covers and replaces any other color; eventually becomes white with dark skin

Dave Howe & Deserito


Photo: Terry Crawford


(NOT a single gene!)

Ajax, owned by Edona Miller
Appaloosa Complex:

leopard, snowflake, varnish roan, blanket, etc.

O (Frame) Overo
Overo for registration purposes includes a variety of color patterns, but the genetic symbol, O, refers to Frame Overo only.
P  Pangare ("Mealy") light golden areas over muzzle, eyes, elbow and flank 
right photo by Judy Goulet
“Belgian”Sorrel, Seal Brown, or "WILD DONKEY" Bay
Rb Rabicano

photo courtesy of


Sb SabinoSabino
Sabino 1 - the sub-type of sabino that is associated with the Maximum White effect

Splashed White

Splash, Splashed White
StySooty/Smutty - black mixed into body coatSooty
ToTobiano, the most common pinto pattern
Dominant White

Pink skin, blue or brown eyes

Karma, Cold Springs HMA Mustang adopted by Andi Harmon of Oregon

Silver dapple - dilutes eumelanin (black pigment) only
bleaches black pigment to brown or blonde


UC Davis, Dr. Ann Bowling

Genetic Formulas and Color Definitions

  • A=Agouti (a = no agouti)

  • Br = Brindle (br = no brindle)

  • C=Non-dilute, fully expressed color pigment

  • Ch = Champagne

  • Ccr=Cream/Creme

  • D=Dun (d= not dun)

  • E and e = the EXTENSION LOCUS, which determines whether or not Black pigment can be expressed
    Dominant "E" allows either red or black (which in reality usually means a BLACK horse, unless other modifiers restrict the black; Recessive "e" allows only Red.

  • Fl = Flaxen mane & tail (fl = no flaxen mane & tail) works only on "ee" red based horses

  • Fr =  Frame Overo (fr = non frame)

  • G=Gray (g = not grey)

  • Lp = Leopard (Appaloosa Complex; New research may prove this obsolete; the many Appaloosa color patterns may be caused by more than one gene)
     lp = no leopard

  • P = Pangare (p = not pangare)

  • Rb = Rabicano (rb = not rabicano)

  • Rn = Roan (rn = not roan)

  • Sb = Sabino (sb = no sabino)

  • Spl = Splash (spl = no splash)

  • -Sty = Sooty/Smutty (-sty = no sootiness)

  • To=Tobiano (to = not tobiano)

  • W=Dominant White (w = not dominant white)

  • Z = Silver Dapples (z=no silver)


Sponenberg uses a more complex and slightly different notation:
  • A = restricts black to points (bay)

  • a=uniform brown/black over entire body

  • B=Black

  • b=brown

  • C=non-dilute, fully expressed

  • cr=cremello dilution

  • D=dun dilution; D dilutes both black and red base colors

  • d=non-dilute, or no dun

  • Ed=dominant Black

  • E=allows black color on points

  • e=red

  • F=red points on ee horses

  • f=flaxen points on ee horses

  • P=Pangare

  • p=non-pangare

  • Sty=Smutty/Sooty= black mixed into body coat

  • sty=clear, non-sooty

  • Z=Silver Dapples: dilutes black to silver dapples; dilutes bay and brown to mimic sorrel; dilutes buckskin to appear near-palomino

  • z=no Z dilution

  • G=grey

  • g=no grey

  • Rn=Roan

  • rn=non-roan

  • T=Tobiano (pinto spotting)

  • t=non-Tobiano, not spotted

  • O=not spotted

  • o=Overo spotted

  • Sb=Sabino spotting

  • sb=non-Sabino

  • Spl=non-splashed White

  • spl=Splashed White

  • Rb=Rabicano

  • rb=non-Rabicano

  • Lp=Leopard (appaloosa complex)

  • lp=no leopard complex

  • W=White

  • w=not white



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