DUN is a "dilution" gene (like Creme, Champagne, Pearl, and Silver Dapples) which modifies (dilutes - think "bleach") but does not fundamentally change the base color.
Dun is a simple dominant, meaning that the color effect is the same whether the individual has one or two Dun genes.
Unlike the other dilutions which tend to dilute the entire horse, dun leaves
a distinctive pattern, allowing the base coat to show through in a specific
pattern that includes a dorsal stripe, horizontal "zebra" stripes on upper
legs, shoulder bars, ear tips, cob-webbing on chest and face, and shaded
face, just as though the
horse were spray-painted with a stencil.
Here's how Dun affects the various Base Colors:
Duns also occur in most wild herds.
ARE DUN HORSES MORE PRIMITIVE, ANCIENT, PURE SPANISH, etc THAN OTHERS?
NO. Dun (along with bay, black, red, roan, the pinto/paint patterns, gray and appaloosa spotting patterns) came to America with the Spanish Conquistadores in the 1500's. Although a wild horse with dun will usually have some "Old Spanish" ancestry (most wild horses do), the presence of dun coloring does not make the horse "primitive" or more "Old Spanish" than any another horse.
Dun is valued for its exotic appearance, and, in both Mustangs and Quarter Horses, it is indicative of at least some Old Spanish lineage. (While some modern non-Spanish horses, such as the Fjord, are also dun, these are not known to have contributed to mustang gene pools)
Dun's association with being "primitive" or "ancient" is likely because some very old breeds of horses, such as Mongolian horses and the very ancient Przewalski's Horse, and some old breeds of European Draft horses, are duns. There is also the matter of the Portuguese Sorraia, which, in terms of its possible contribution to American Mustang populations, is unlikely, although the theory has some strong proponents.
Bottom line is - Dun is a color. There is nothing primitive about today's modern dun-colored horses.
Rhonda Groves and Oregon (non-Kiger) dun mustang, "Latte"
Divide Basin (Wyoming) HMA
Andi Harmon's Lobo Dun (dark grulla, black drugs) mare, "Star"
Gus, day adopted by Sherry Timm - note yellowish baby coat
Two years later, Gus in full Grullo coloring
Grullo Overo gelding at National Wild Horse & Burro Show, Reno, NV, June 2001
Soft Coffee-Cream Grulla mare and foal at Palomino Valley
|Black-based Grullo foals often start out yellowish, and darken as they mature.|
This yellow-ish colt shed out to full-fledged Grullo.
DUN vs COUNTERSHADING: Some horses appear to have a dorsal stripe, but it either disappears upon maturity, or with seasonal shedding. This coloring is called called "counter-shading", a function of the "Sooty" gene, and it can be confusing to horse owners. See this link for more: Sooty Foals and Countershading
Bays commonly have a "line-back" which, although it appears to be a true dorsal stripe, is not Dun.
Dun is a term often used to mean buckskin, and vice versa. For some breed registry associations that is a correct usage. For mustangs, the term Dun refers to horses with dun factor markings only. Here is a great website about this issue: BUCKSKIN vs DUN
Spirit, Stallion of the Cimarron