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 and prefer pictures of wild, or formerly-wild horses wherever possible.

COMMON GENETIC NOTATION White boxes denote notation used by Sponenberg, but not by Bowling and others
Gene	Name & What it does	Result
A	Agouti (Bay Modifier): Acts on "E" to restrict eumelanin  to points; No effect on "e" or red	Bay
C	Non-dilute	Full Color
Ccr	Creme: 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
Ch	Champagne: 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
D	Dun dilution - dilutes both eumelanin and phaeomelanin	Dun on Red = Red Dun Dun on Bay = Dun, Zebra Dun, Bay Dun, Classic Dun Dun on Black = Grulla/o
d	Non-dilute	Full Color
Ed, E+	Dominant black, epistatic to A locus	Black
E	Dominant 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
Ranger and Karen Blackwoode	Recessive form of "extension" locus; Allows Phaeomelanin (red pigment)only;  epistatic to A locus	Red (chestnut, sorrel)
F	Red points on ee horses	Tostado or alazan
f	Flaxen points on ee horses (This is Sponenberg notation)	Ruano
Fr	photo: Ginny Freeman 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 no one uses it. So a frame overo is Oo, and solids are oo.	Frame Overo Also: Overo Lethal White Syndrome
G	Grey - gradually covers and replaces any other color; eventually becomes white with dark skin	Dave Howe & Deserito Grey
Lp	Photo: Terry Crawford Leopard (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, for Overo, 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 arabianrun.com	Rabicano
Rn	Roan	Roan
Sb	Sabino	Sabino
Spl	photo by Marlene Maki Splashed White	Splash, Splashed White
Sty	Sooty/Smutty - black mixed into body coat	Sooty
To	Tobiano	Tobiano
W	White	Dominant White Pink skin, blue or brown eyes
Z	Karma, Cold Springs HMA Mustang adopted by Andi Harmon of Oregon Silver dapple - dilutes eumelanin only	Converts black to brown with white mane and tail