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Appaloosa Genetics Essay

By Mattie Cowherd

Spotted coat colors are ancient in the horse world. They may have first originated in Southern France but quickly spread throughout the world, including the Americas when the Conquistadors brought spotted horses with them to the new world. (Scott, “Genetics”) Today numerous breeds, including the Appaloosa, the Noriker, and the Pony of the Americas are identified through their spotted coats.

The classic spotting comes from the Leopard Gene (LP), which may be one single gene or a complex of genes (UC Davis). Currently there is no formal test for this gene. Spotting can be found in any breed but is most common in the spotted breeds such as the Appaloosa (hence the name). However, overo and other paint genes will cover the spotted gene (Wikipedia, “Appaloosa”). The spotting genes cover or modify the basic coat color. Also, spotted horses classically have white sclera, mottled skin pigment, and narrowly striped hoofs. Striped hoofs and white sclera are noticeable at birth, while only 1/3 of spotted horses are born with mottled skin pigmentation. The pigmentation can be acquired later. (Gower, 101-102).

The LP gene is incompletely dominant (Wikipedia, “Leopard Complex”) and when the gene is present in the dominant form, appaloosa characteristics will be found. The E (red) gene suppresses the white effect of the LP gene to some extent, but the A (agouti/bay) gene lessens the effect of the E gene (SheilaArcher). The Leopard complex is the most complex of the color genes and is not fully or well understood. The LP gene is also enhanced by modifiers. These modifiers are quantified additives, so the more modifiers that a horse possesses, the more colorful it will be. Sex can also effect how much color a horse will show. Colts normally color more than fillies. (Gower, 102-103).

Appaloosa horses can have a variety of coat patterns. The most dominant of these patterns is the few-spot leopard, which when bred to another few-spot, will produce color 100% of the time in all of the spotted coat patterns except mottled. The few-spot is considered true breeding, and will produce color when bred even to solid horses 99.9% of the time. The other spotted colors, in descending dominance, are: leopard, varnish, blanket, snowflake, frost, and mottled. All of these colors, with the exception of the few-spot, will produce color 50% of the time when bred to solid horses. (Gower, 101-103; Scott, “Appaloosa Horses”; Wikipedia, “Appaloosa”)

The spotted patterns can be divided into four general colors: snowcap, dark spots, snowflake, and varnish. Each of these is discussed in more detail below.

The snowcap pattern is formed from the ScS allele of the LP gene. This allele prevents pigment formation and white appears. The most basic form of snowcap is white with pink skin over the hips or a snowcap blanket. However, the white can be minimal or cover most of the horse. If the horse is mostly white, the snowcap has covered all but (usually) a few minimal spots on the body and the legs. These are the few-spot appaloosas and are considered true breeding. However, the snowcap also has the associated effects of night blindness. (Gower, 103-104). Studies are currently underway to better understand this genetic link between snowcap and night blindness (SheilaArcher).

Dark Spots are caused by the SdS allele of the LP gene. This allele causes dark spots to appear. These spots may be small or as large as a fist. They tend to not be perfectly round, but rather oval shaped, and can appear with or without halo effects. These spots tend shape themselves in the direction of the hair. Some horses may only have dark spots, which will be the same color or darker than the base color. Others will have dark spots in combination with the other spotting characteristics, including spotted blanket. (Gower, 104). (Scott, “Appaloosa Horses; Wikipedia, “Appaloosa”).

The Snowflake pattern is caused by the SnS allele of the LP gene. It causes small white speckles and white spots. These spots may not be evident at birth, may move around as the horse ages, and becomes more prominent with age. This pattern can be as minimal as a patch of lace on the hips or be as extensive as full body covering with little white on the head. (Gower, 105). (Scott, “Appaloosa Horses; Wikipedia, “Appaloosa”).

Varnish, the last of the basic patterns, is caused by the SvS allele of the LP gene. Varnish is a non-spotting gene that causes progressive silvering over the body with color left on bony prominences. It can look and be mistaken for roan except that it is not always evident at birth and is progressive like the gray gene. The homozygous form of this allele is thought to be lighter than the heterozygous form. It can occur over the whole body, progress from the forehead back, or can just cover the rump. (Scott, 104-106). (Scott, “Appaloosa Horses; Wikipedia, “Appaloosa”).

Though the color itself is not completely understood, spotting is present in horse coat colors. It can cause some very stunning and interesting coat patterns. As research continues, we may one day better understand the appaloosa color and how it is affected genetically.

Resources:

    Gower, Jeanette. Horse Color Explained. Pages 101-108. Talfalgar Square Publishing, North Pomfret, Vermont. 2000.

    SheilaArcher. “The Appaloosa Project: Studies Currently Underway”. <http://www.appaloosaproject. info/index.php?module=pagemaster&PAGE_user_op=view_page&PAGE_id= 1&MMN_position=5:5>. The Appaloosa Project. 2007-2008. Last modified on October 31, 2008.
 
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