The dun gene is one of the dilution genes that affects both red and black pigments in a horse's coat color. Unlike the silver dapple gene (which works only on black-based coats) or the creme gene (works on red-based coats), it has the ability to affect the appearance of all black, bay, or chestnut (red) based horses to some degree.

The dun gene does not cause the horse to look any different when it is present in two copies (one from both parents) than one copy (one from only one parent).

The gene affects coat color by turning black to chocolate, and red to gold.

See Equine coat color genetics to compare the genes.

Dun vs buckskin

Since dun closely resembles buckskin when it is on a bay-based (black base + Agouti gene) horse, it is commonly confused with buckskin. The difference between these two genes is the dun gene also causes primitive markings. Primitive markings include:

• Shoulder blade stripes
• Dorsal stripe
• Zebra stripes on legs
• Cob webbing

These primitive markings are usually a shade or two darker than the body color.

However, dorsal striping does not guarentee that the horse carries the dun gene. The counter-shading gene can also produce dorsal striping in breeds such as the Arabian and the Thoroughbred, where the dun dilution gene is does not exist in the gene pool. You can see examples of "false duns" and countershading at http://www.duncentralstation.com.

http://www.norsire.com/

http://www.goldhopefarm.com/

Shades of dun

The Dun gene seems to have more concentration in the body (so lightens the body coat more) than the mane, tail, legs and head. This would explain why points on a dun are a shade darker than the coat, or in the case of a Zebra Dun, the mane, tail, and legs are not diluted much at all. The Zebra Duns have the "buckskin" look to them: tan body color with black points, plus the primitive markings. Their coat, however, is usually more tan than the yellow of most buckskins. Red Dun colored horses do not have the black points, and they are usually grouped together and called Red Duns. Grullo (GREW-yo)* colored duns have a smoky, bluish, or mouse-brown color and can vary from light to dark. They consistently have black points and they have a dark or black head, which is an identifying characteristic of the Grullo group. The primitive markings are usually all black.

• Note: because Grullo is a Spanish word, mares are referred to as grulla (GREW-ya), and males as grullo (GREW-yo)

Breeding and the dun gene

• Red base + Dun= Red Dun (it is because they are red-based that they don't have black points of the Zebra Dun). Less common than Zebra/bay Duns, more than Grullos
• Black base + Dun= Grullo or Grulla. The most rare form of dun coloring
• Bay (black base = Agouti gene)= Zebra Dun/ Bay Dun.