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Somewhere Under The Rainbow By Elsie Darrah
Editor’s Note: This is the first in a series of articles that will help you to better identify horse colors, dilutions, modifiers and patterns plus understand how they come about. Understanding horse color enables us to identify horses correctly. Accurate identification of a horse's color is the key ingredient in understanding the genetic basis of color. We all recognize that in the Tennessee Walking Horse breed there is a Rainbow of colors. A horse's ultimate color results from the interaction of multiple independent processes involving genes which can dilute, modify, restrict color or add white over solid colors. It’s like using building blocks to create a unique individual from a rainbow of colors. TWHBEA’s updated Colors and Markings brochure recognizes 16 colors: black, smoky black, smoky cream, classic champagne, classic cream champagne, bay, brown, buckskin, perlino, amber champagne, amber cream champagne, chestnut, palomino, cremello, gold champagne, and gold cream champagne. All of these colors are derived from two basic colors, red or black. Although bay isn’t a base color we chose to include bay in the lineup because it simplifies the explanation of how each of the colors are derived. White is available for a color choice but a true white horse is rare and most TWHs registered as white are maximum sabinos. Two additional dilution genes, dun and silver, can be combined with any of the 16 colors and affects those colors in many different ways. Two color modifiers, roan and grey, can also interact with any of the 16 colors and the additional dilution genes. Color patterns, tobiano, sabino, overo or a tobiano/sabino combination superimposes white over what would have been a solid color. THE BASE COAT COLOR GENES Everything that you see, and consider a different color, is actually the result of modifying genes added to the base color of RED or BLACK. These modifying genes change the appearance, or phenotype, of the horse but the horse’s BASE COLOR is still RED or BLACK. Black (noted as "E") is dominant to red (noted as "e"); chestnut/red is recessive to black. This means that if a horse has at least one black gene, it will be black (or a black based color). It needs (2) two red genes (thus no black gene at all) to be red (or any red based color). In other words, black "covers" red. Black horses can be described as having black bodies and black points. Black TWHs are common in the breed and comprise 36% of all horses registered with TWHBEA. Non-Fading Black is just as it sounds, a Black horse that does not become "sunburned" or fade from effects of sun and weather. The horse shown in the photo above is an excellent example of the non-fading shade. He is a working ranch horse who spent his life out in the elements. As you can see from the photo, this horse has not faded from sweat, saddles rubbing or weather. These foals may be born a smoky or blue-black shade. At maturity these horses very rarely will ever fade, only in extreme conditions. Fading Black is a horse that fades from sun and weather such as the horse pictured in the photo on the left. These foals are usually born a smoky ashen color, but may also be born a dark bay or brown. Mature horses usually fade to varying degrees and maintaining the rich, deep Black color requires a lot of work.
Regardless of whether they will fade or not when mature, your average black foal will be a black color with lighter sooty areas along the underside of its body. It's normal for a black foal to have light colored legs. Chestnut and Sorrel are terms used to classify horses with red bodies and red points (mane, tail, ear rims, and legs). Depending on who you talk to, you will probably get a different opinion regarding what is the correct term to describe this color. However, genetic experts as well as scientific evidence have proven that genetically, Chestnut and Sorrel are controlled by the same genes, therefore making them the same color, regardless of shade. So all horses with a red pigment base and points will be referred to as Chestnut or Chestnut based in these articles. Chestnut TWHs make up 27% of the TWHBEA registry. Chestnuts are usually easily identified. The genetic explanation of chestnut is also very easily understood. Chestnut horses have reddish tinted body coats ranging from very light to very dark. The mane and tail can range in color from "white" or flaxen to very dark, so dark they look black.
Sometimes the mane and tail can have a "sunburned" look. This is especially confusing when it is on a very dark horse. The points are usually the same color as the body coat or will vary a shade or two, but these are never black. Chestnut horses can not make black pigment.
Point color can vary on red based horses. The darkest manes and tails of such horses can be nearly black, but the lower leg will remain red so these horses cannot easily be confused with Bay. The next shade of manes and tails is a dark brown and the next being red and the next being blonde to flaxen. Although bay isn’t a base color we chose to include it in our discussion of base colors because it simplifies the explanation of how many of the black based colors are derived when affected by our first and most common modifier, the Agouti, or as it’s commonly called, the "bay gene". The Agouti gene produces bay horses by restricting the black color to the points, In other words, bays and browns are black horses with a dominant modifying gene called Agouti.
This allows the red that is "uncovered" by Agouti to show through on the body of the horse. Chestnuts can carry Agouti, but it won't show on them as they have no black hair to restrict to the points. They can, of course, pass it on to their offspring. Black horses cannot have Agouti, because if they did, they'd be bay and not black. For example, a black X chestnut cross might produce a bay foal. This would happen when the Agouti, or bay gene, came from the chestnut parent, and the black base color came from the black parent. Brown, or what is sometimes called "seal brown", is a nearly black horse with reddish areas on the muzzle and flanks. There is a lot of crossover in phenotype (appearance) between very dark bays and browns. At this time there is no way to distinguish bay from brown when color testing.
The genetics of coat color is complicated and the science of color is an ongoing process. Ten years ago we didn't have any of this information and now with coat color testing available we can pinpoint the true colors of horses.
Genetic Terms AGOUTI |
