Equine Color Genetics Part 2
By Triple Crown Nutrition Intern Rachel Voelker
This blog is a continuation of The Basics of Equine Color Genetics. If you are new to equine color genetics, I would recommend reading my first blog. I will discuss the base coats of horses and the various color modifiers and patterns for this blog.
Base Coat Colors
Horses have 3 base coat colors – red, black or bay.
- The Extension gene controls whether the horse will be red (e) or black (E).
- The interaction of Extension and Agouti controls whether the horse will be bay or not.
- Agouti makes the horse bay by forcing the black pigment to the points of the horse (tips of ears, mane, tail, and legs).
- At the Extension gene, a black horse would have the genotype of (E/E) or (E/e) and a red horse would have a genotype of (e/e).
- A bay horse has to have a black base. If black is not present, Agouti cannot force the black to the points.
- Therefore, the genotype of a bay horse is (E/E or E/e and A/A or A/a).
- A red horse can have dominant agouti but it will not be expressed in the coat. The genotype of a red horse can be (e/e and A/A, A/a, or a/a). A red horse that carries dominant agouti (A) can produce a bay foal as long as the other parent passes black (E) to the foal.
Base Coat Modifiers
The rest of the modifiers and patterns in horses build on these base colors. They all have a dominant form of inheritance. Therefore, if a horse does not have the dominant gene for a certain pattern or modifier, it cannot be expressed in the coat or passed on to the offspring. Modifiers affect the appearance of the color of the horse while patterns add white markings into the coat.
Here are descriptions of each modifier or pattern and examples:
- Gray is a dominant color and if present, will cause the pigment of the hair to turn white over time. The color genetics of the color that turned white remain. For example, our stallion, was a black dun before he turned gray. He still can produce dun offspring. A parent must have a dominant gray gene to produce an offspring that turns gray. Their genotype would be (n/G). A non-gray horse would be (n/n) for gray. Homozygosity does not affect appearance.
Grey (Black Dun) Missouri Fox Trotter Stallion, Color Tested E/e, a/a, D/nd2, n/G
- Roan is a modifier that affects the body color of the horse. The head, mane, tail, and legs will stay dark while the body will have white hairs mixed in. A non-roan horse would be (n/n) for roan. Homozygosity does not affect appearance.
Blue Roan Missouri Fox Trotter Filly, E/e, a/a, n/Rn
Red Roan Missouri Fox Trotter Stallion, e/e, a/a, n/Rn
- Dun dilutes the body color and adds a dorsal stripe down their back. It can also add leg and shoulder barring. A non-dun would be (n/n) or (nd2/nd2) for dun. A horse with dun (D) displays body dilution as well as primitive markings and can pass it to their offspring. However, there is a form of dun where the physical appearance is in the coat, but it cannot be passed onto offspring and is referred to as (nd1). A horse with (nd1) is considered non-dun. Homozygosity does not affect appearance.
Bay Dun Missouri Fox Trotter Stallion, Color Tested E/e, A/a, D/nd2
- Silver only affects black pigment like agouti. Silver dilutes the mane and tail and lightens the body color. Sometimes it is referred to as silver dapple because it can add dapples to the body. A red horse can carry silver but it will not show in their appearance. A non-silver horse is (n/n) for silver. Homozygosity does not affect appearance.
Silver Black Sabino Tennessee Walker Mare, E/e, a/a, n/Z, n/Sb
- Champagne dilutes the body color and adds a sheen to their coat. They will have freckled skin and have green or amber eyes. In its homozygous form, the skin stays pink instead of getting freckles and the body color is diluted even more. A red with champagne is called gold champagne, a bay with champagne is called, ‘amber champagne’ and a black with champagne is called, ‘classic champagne’. A non-champagne is (n/n) for champagne.
Gold Cream Champagne Missouri Fox Trotter Mare, Color Tested e/e, A/a, n/Ch, n/Cr
Amber Champagne Tobiano Tennessee Walker Mare, Color Tested E/e, A/a, Ch/Ch, n/To
- Cream dilutes the body color, red becomes palomino, bay, becomes buckskin, and black because smokey black. In its homozygous form, the skin becomes pink, the eyes become blue, and the body color is creamy white. Red with homozygous cream is called cremello, bay with homozygous cream is called perlino, and black with homozygous cream is called smokey cream. Each form of homozygous cream can look very similar. A non-cream horse is (n/n) for cream.
Buckskin Tobiano Missouri Fox Trotter Mare, E/e, A/a, n/Cr, n/To
Palomino Missouri Fox Trotter Mare, e/e, n/Cr
- Tobiano is a white pattern that usually adds some facial white, white stockings and white spots going over the back of the horse. There is a wide range of patterns tobiano can put on a horse. Tobiano is a very common white pattern. Homozygosity does not affect appearance. A non-tobiano horse is (n/n) for tobiano.
Black Tobiano Missouri Fox Trotter Stallion, Color Tested E/E, a/a, n/To
Black Tobiano Missouri Fox Trotter Mare, E/E, a/a, n/To
- Sabino is a white pattern that usually will cause wide blazes, white stockings and belly spots with uneven edges. It can also cause some roaning in the coat. There is a large variation in pattern. In its homozygous form, the horse will be almost all white and is called a max sabino. Sabino is not lethal in homozygous form. A non-sabino horse would be (n/n) for sabino.
Smokey Black Sabino Missouri Fox Trotter Mare, Color Tested E/e, a/a, n/Cr, n/Sb
Red Sabino Missouri Fox Trotter Mare, e/e, n/Sb
Splashed White (SW)
- Splash creates a similar pattern to sabino, but with smoother edges. There are four forms (SW1, SW2, SW3, SW4). SW1 is most common and found in several breeds. SW2, SW3, SW4 are limited to Quarter Horses, Paints, and Appaloosas. Some forms can cause deafness or be lethal in the homozygous state. A non-splashed white horse is (n/n) for splashed white.
Classic Champagne Sabino Splashed White Missouri Fox Trotter Mare, Color Tested E/e, n/Ch, n/Sb, n/SW1
- Frame, adds white patterns to the sides of the horses and to the neck, it does not cross over the back. It can also be completely hidden and not express any pattern at all. It is lethal in its homozygous form. A non-frame horse is (n/n).
Red Frame Missouri Fox Trotter Mare, Color Tested e/e, n/O
This mare most likely carries some other white patterns like sabino or tobiano but has not been color tested for them.
Buckskin Frame Missouri Fox Trotter Mare, E/e, A/a, n/Cr, n/O
Dominant White (W)
- Dominant white is in certain bloodlines of certain breeds of horses. They can cause the horse to be all white. Ther are several different dominant white patterns. A non-dominant white horse would be (n/n) for dominant white.
Appaloosa (LP or PATN1)
- Appaloosa or leopard complex spotting pattern produces a variety of patterns and has more of an effect in the homozygous state. A non-appaloosa horse would be (n/n) for Appaloosa.
*n means that there is no recessive form of the gene to be passed.
All of the horses pictured are owned by Copper Ridge Gaited Horses.
Did you miss part 1 about studying color genetics in horses? Check it out here > http://bit.ly/colorgenetics