The Dun gene is a dilution gene that affects both red and black coat color pigments. The gene is associated with "primitive marking" and has the ability to affect the appearance of all black, bay, or chestnut ("red")-based horses to some degree by lightening the base body coat.
The dark stripe down the middle of the animal's back is the most recognizable marking associated with Dun horses. Other markings include a tail and mane darker than the body coat and usually darker faces and legs. The classic Dun is a gray-gold or tan, characterized by a body color ranging from sandy yellow to reddish-brown. Depending on other underlying genetic coat color factors, a Dun horse may appear a light yellowish shade or a steel gray. Manes, tails, primitive markings and other dark areas are usually the shade of the non-diluted base coat color.
The Dun allele is dominant, meaning that a horse that carries either a single copy (heterozygous) or two copies (homozygous) of the gene will exhibit a dun phenotype. Unlike the silver dilution gene (which affects only black-based coats), the Dun gene affects both black and red-based horses.
The Dun dilution gene is characterized by markings which are darker than the body color. These markings include:
- The Dorsal stripe (stripe down the center of the back, along the spine), seen almost universally on all duns.
- Horizontal striping on the back of forelegs, common on most duns, though at times rather faint.
- Shoulder blade striping, the least commonly-seen of the primitive markings.
Quarter Horses, Paints, Appaloosas, Icelandic Horses, Norwegian Fjords, Paso Finos, Peruvian Pasos and many pony breeds
|Base Coat||Common Coat color|
|Red (chestnut) base||+ Dun gene||Red dun|
|Black base||+ Dun gene||Blue dun, mouse dun or Grullo/Grulla.|
|Bay (black base + Agouti gene)||+ Dun gene||Classic dun, sometimes called "Bay dun" or "Zebra dun"|
Animal Genetics offers DNA testing for Dun coat color. The genetic test verifies the presence of one or two copies of the Dun mutation and presents results as one of the following:
|D/D||Homozygous||Horse will always produce a Dun foal|
|D/d||Heterozygous||Horse tested Heterozygous for Dun and will pass the Dun gene on to its offspring 50%|