"Dominant" means simply that a horse needs only one gene (in a pair) for a particular trait in order to exhibit it. If the horse has one gene, it will exhibit that trait. (The extent to which the trait is exhibited can be modified by the presence of other dominant genes - but it WILL express itself!)
Technically, Genes themselves are not dominant or recessive, although we speak of them as such.
Alleles are dominant or recessive. For example, the MC1R gene (called Extension) codes for the production of eumelanin pigment, causing a horse to be black. A mutation occurred in that gene at some time long ago, such that the gene now coded for the production of phaeomelanin, which produces red pigment. If a horse carries one copy of the unmutated gene, and a second copy of the mutated gene, the unmutated gene creates enough eumelanin to mask the other copy. Therefore, we say that the unmutated copy, or allele (E) is dominant to the mutated copy, or allele (e).
The same is true for all genes: cream, tobiano, overo, dun...is the mutated allele dominant or recessive? But the gene is just a gene.
It is generally not possible to tell from appearances alone whether the horse is homozygous (both genes are the same for a trait) or heterozygous (only one gene for the trait). Exceptions to this are the Lethals, where being homozygous for a trait (Frame and White) is lethal. In these cases, the foal either dies before birth, or soon after.
The other exception occurs with the Creme dilution gene, which acts as an "Incomplete Dominant." With an "incomplete dominant", you get one effect from one gene, and an exaggerated effect from a double dose. Thus, one creme gene on a red base creates Palomino; Two creme genes create Cremello (a further diluted state)
|Base Color||One Creme Gene||Two Creme Genes|
|Black||Smoky Black||Smoky Creme|
Both Appaloosa and Tobiano horses sometimes show visual clues to their homozygous state, although genetic testing is the only sure way to know (if you care)
A horse bearing multiple dominant genes will exhibit multiple traits.
Red and Flaxen are two of the very few Recessives. Flaxen only affects Red. A black horse with the Flaxen gene will show no flaxen effects. Because both are Recessive (their trait is only expressed if both allelles on the gene pair are the same) Chestnut and Flaxen Chestnut horses are able to breed true. Because Red can "hide" for generations, until bred to another horse with a hidden recessive red gene - breeders (Freisian, Percheron, etc.) who desire only black horses have a problem. UC Davis has a simple test for the red gene, which is a useful tool.
Other Pages In the Color Section of this Website:
The Major Sub-Sections of the Color part of this website are:
A Quick Overview of Horse Genetics
Horse Color Genetics Charts 2
Equine Base Colors
Dominant Horse Color Genes
The Dilution Genes
Recessive Color Genes
Miscellaneous Color Issues
Equine Base Colors includes:
Black l Red (sorrel, chestnut)
Within Dominant Color genes you will find these sub-chapters:
Agouti/Bay Black Gray Pangare White Spotting Patterns Roan Rabicano Sooty
Although most of the Dilution Genes are dominants (Creme is "Mixed Dominant"), they have their own section:
The Dilution Genes includes:
Champagne Creme Dun Pearl Silver
Subchapters of Creme inlcude:
Single Dilutes: Palomino, Buckskin, Smokey Black
Double Dilutes: Cremello, Perlino, Smokey Cream
White Spotting Patterns includes:
The Appaloosa Complex Tobiano The Overo Complex
The Overo Complex includes:
Frame Sabino Splash Tovero
plus a page about
How to Tell the Overos Apart
Frame includes a special page about Overo Lethal White Syndrome
Recessive Color Genes includes:
Miscellaneous Color Issues includes:
Brindle Brown Curly (not a color, but...) White Dun or Buckskin?
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.
Disclaimer: I am not a geneticist. The information on these color pages represents the best scientific info I have been able to locate. Theories and knowledge change over time, and it may be you know something I don't - this site is not intended to be "the last word" in colors, just a guide for those wishing to explore the topic.