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Getting Informed…About
Duns
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Visit Enloe Quarter Horses/Horse Color Genetics Message Board
to post color questions!
Duns
are one of the trickier coat patterns in the quarter horse world. Duns are
often referred to as "line-backed buckskins" and about every shade description
of color imaginable. A few examples include "Buttermilk Dun", "Claybank
Dun", "Bronze Dun", and "Peach Dun". In order to be considered a Dun
by the American Quarter Horse Association, the horse must
exhibit dun factor traits including a dorsal stripe down the back and have black
points (mane, tail, legs). Although Duns are generally thought to
have a diluted coat color, the coat shade
can actually range from a buttermilk cream to a near blood bay color.
The stallion pictured at left is Mr Blackburn 012.
He is the product of a red dun stallion and a dark, almost bay looking dun mare.
He shows all dun factors prominently (see
description of dun factors below).
Especially note the striping on the neck, the dorsal down the back and the very
striking zebra stripes on the legs. Mr Blackburn 012 is a lighter than
average dun and may be homozygous for dun factor. Read on for further
details regarding genetic make-up.
Genetics behind the color
Quick
genetics lesson - Genes are located on strands of DNA. Two alleles
meet at a specific point (called a locus) to form a gene. A foal receives an
allele for a gene from each parent. The two combine and you have a
gene. At this time, data on the horse has not been mapped for
all genes. Therefore, much of the data and analysis available is an
educated guess based on progeny tests rather than actual allele/gene
analysis. The following genetic description comes from the University of
California - Davis, a leader in equine genetic research.
The genetic mapping of a Dun horse's color is believed by the University of California-Davis to be
E? D? CC? A? rr gg
where each grouping represents a gene and capital letters are dominant, small letters are recessive, and ? may be either dominant or recessive. The exception is the Creme gene C, which is Ccr in dominant form, C in recessive form. Dominant alleles mask recessive alleles, meaning recessive alleles will only be displayed when they are in the homozygous form.
The tricky part about duns are the genetics. The important thing to remember about duns is Dun Factor vs. Creme Gene. These are two separate genes and are inherited separately. Dun must have the dun factor gene. The actual shade of dun can vary greatly depending on family inheritance. Duns can hide a recessive Agouti (a) (required for black, grulla and blue roan horses). It can also hide the creme gene (Ccr) (required for palomino, dunalino, buckskin, cremello, perlino and smoky black). The Dun gene normally dilutes a horse's body coat to a lighter color, gives the horse a defined dorsal stripe, and adds several or all the other dun factors to the horse's body. The Dun gene changes a sorrel to red dun, a palomino to dunalino, a black to grullo, and a bay or brown to dun. A dun may carry one (heterozygous) or two copies (homozygous) of the Dun allele.
What are these genes?
Duns can be produced by a variety of different colored parents. The key ingredients to reproducing the dun color is at least one parent with a black points and dun factor, and at least one parent with a dominant Agouti gene. You can not produce a dun by breeding horses without dominant Agouti genes (black, grulla and blue roan) to other horses without dominant Agouti genes. For example, two grullas will NEVER produce a dun foal. The filly pictured at right is the result of a suspected homozygous dun factored grulla mare crossed with a red dun stallion. We know this filly's genotype is Ee Aa D? rr gg CC . The only unknown factor is if she is homozygous dun or not. She received her black points and dun factor from her mother, and the dominant Agouti and possibly dun factor from her sire. Because her dam is a suspected homozygous dun with 10 dun factored foals, this filly has a 50% chance of being homozygous for the dun gene.
It should also be noted that some foals are born
with a dun look to them and they actually shed off grulla. These foals
usually look a suspicious dun color and are often the product of one sorrel or
bay parent.
Samples of Dun Horses
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Additional web sites with genetics information:
University of California-Davis: http://www.vgl.ucdavis.edu/~lvmillon/
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