Dun gene
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The dun gene is a dilution gene that affects both red and black pigments in the coat color of a horse. The dun gene 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 and suppressing the underlying base color to the mane, tail, legs and "primitive markings."
The classic Dun is a gray-gold or tan, characterized by a body color ranging from sandy yellow to reddish-brown. Dun horses always have a dark stripe down the middle of their back, a tail and mane darker than the body coat, and usually darker faces and legs. Other duns may appear a light yellowish shade, or a steel gray, depending on the underlying coat color genetics. Manes, tails, primitive markings and other dark areas are usually the shade of the non-diluted base coat color.
The dun allele is a simple dominant, so that the phenotype of a horse with either one copy or two copies of the gene is dun. It has a stronger effect than the silver dapple gene, which acts only on black-based coats, or the cream gene, an incomplete dominant which must be homozygous to be fully expressed, and is visible when heterozygous only on bay and chestnut coats, and then to a lesser degree.
The dun gene also causes "primitive" markings which are darker than the body color. Primitive markings include:
- Dorsal stripe (stripe down the center of the back, along the spine), seen almost universally on all duns
- Zebra stripes on the back of forelegs, common on most duns, though at times rather faint.
- Shoulder blade stripe, the least commonly-seen of the primitive markings
Dorsal striping does not guarantee that the horse carries the dun gene. A counter-shading gene can also produce faint dorsal striping in bays and chestnuts, even in breeds such as the Arabian horse or the Thoroughbred, where the dun gene is not carried in the gene pool. However, virtually all duns have the dorsal stripe, most have the leg striping, and the shoulder stripes are often fainter, but usually visible on horses with a short summer hair coat.
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[edit] Shades of dun
- See also: Equine coat color genetics and Equine coat color
The dun gene has a stronger dilution effect on the body than the mane, tail, legs and primitive markings, and so lightens the body coat more. This explains why points on a dun are a shade darker than the coat, or in the case of a "classic" dun, the mane, tail, and legs are often black or only slightly diluted.
- Dun, also called Bay dun or "zebra" dun. The most common type of dun, has a tan or gold body with black mane, tail and primitive markings. Genetically, the horse has an underlying bay coat color, acted upon by the dun gene.
- Red dun horses do not have black points, as there is no black on the horse to be affected. Instead, the points and primitive markings are a darker shade of red than the coat. Genetically, the horse has an underlying chestnut coat color, acted upon by the dun gene.
- Grullo (GREW-yo, or Grulla, GREW-ya), also called blue dun or "mouse" dun, have a smoky, bluish, or mouse-brown color and can vary from light to dark. They consistently have black points and they often have a dark or black head, which is an identifying characteristic of the this color. The primitive markings are usually all black. Genetically, the horse has an underlying black coat color, acted upon by the dun gene. Unlike a roan, there are no intermingled black and white hairs, and unlike a true gray, which also intermingles light and dark hairs, the color does not change to a lighter shade as the horse ages. With a dun, the hair color itself is one solid shade.
[edit] Dun vs buckskin
Since the dun gene, when on a "bay dun" horse, can closely resemble buckskin, in that both colors feature a light-colored coat with a dark mane and tail, classic duns are frequently confused with buckskins. The difference between these two colors is that dun is a tan color, somewhat duller than the more cream or gold buckskin, and duns also possess the primitive markings. (Though a few buckskins do show a dorsal stripe.)
Genetically, a bay dun is a bay horse with the dun gene that causes the lighter coat color and the primitive markings. A buckskin is bay horse with the addition of the cream gene causing the coat color to be diluted from red to gold, without primitive markings.
To further confuse matters, it is possible for a horse to carry both dun and cream dilution genes; such horses with golden buckskin coloring and a complete set of primitive markings is referred to as a "buckskin dun" or a "dunskin." On such horses, the distinctive markings of a dun can be more noticeable during the summer months when the winter hair sheds.
[edit] Breeding and the dun gene
- Red (Chestnut) base + Dun gene= Red Dun (horses do not have black points of the classic 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").
The three different dun varieties usually occur in proportion to the occurrence of the corresponding base colors in each particular breed. Other variations result from the interplay of additional genes. For example:
- Bay + Dun + cream gene = "dunskin" or "buckskin dun"
[edit] See also
- Equine coat color
- Cream gene
- Buckskin (color)
- Bay (color)
- chestnut (coat)
- black (horse)
- Equine coat color genetics
- Dilution gene
[edit] References
- "Introduction to Coat Color Genetics" from Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis. Web Site accessed January 12, 2008
- Dun Zygosity test from Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis. Web Site accessed January 12, 2008
- Dun Horse Shades: Grullo, Red Dun, Bay Dun & Photos
- Dun Factors: Dorsal Stripe, Leg Barring, etc.
- Examples of "false duns" and countershading
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