Thursday, September 20, 2007

Colors that do not exist in purebreds


Arabians are crossed with other breeds to produce half-Arabians with additional colors. Purebred Arabians never carry dilution genes such as the dun gene, nor the cream gene. Because they do not carry any dilution genes, purebred Arabians cannot be cremello, perlino, palomino or buckskin. Arabians also never carry the proposed "dominant white" (W) gene that produces a true white horse (with pink skin and blue or light-colored eyes).
Purebred Arabians today do not possess genes for most spotting patterns, such as
pinto or Appaloosa, except for sabino, discussed below. Spotting or excess white was once thought by some to be a sign of "impure" blood, was disfavored by Arabian breeders, and believed by some to be a mark of impurity until DNA testing for verification of parentage became standard. For a time, horses with belly spots and other white markings deemed excessive could not even be registered, and even after the rule was softened, excess white was sometimes penalized in the show ring. Nonetheless, there is pictorial evidence from depictions of chariot horses in Ancient Egypt and some later artwork that suggests that some of these patterns may have existed in antiquity.
Thus, though the purebred Arabian produces a limited range of potential colors, there is also a positive result: because they never carry the white gene ("W") or the
frame overo gene ("O"), they can never produce foals with lethal albino or lethal white syndrome. (Though a partbred could carry these genes if the non-Arabian parent was a carrier). Sabino in the Arabian.One spotting pattern, sabino, does exist in purebred Arabians. The sabino gene (or gene-complex), produces white markings such as "high white" on the legs (above the knees and hocks), irregular spotting on the legs, belly and face, white markings that extend beyond the eyes or under the chin and jaw, and occasionally, roaning. While, many Arabians meet the definition of having minimal to moderately expressed sabino characteristics,Sabino Arabians, particularly those that appear to be nearly white, are controversial.
Today, some researchers call "Sabino-white" horses - those that are over 90% white (with pink skin) - "maximum" sabinos. "Sabino-white" is exceedingly uncommon, possibly exhibited by as few as eleven Arabians worldwide. Some groups consider a "Maximum" Sabino to be a horse that is over 50% white. In either case, studies at the
University of California, Davis indicate that the gene (or genes) which produces sabino in Arabians does not appear to be the autosomal dominant gene "SB1" or "Sabino1," that often produces completely white horses in other breeds. To date Arabians do not appear to carry it.((Rabicano or roan)).Another unusual color pattern seen on rare occasions in Arabians is rabicano. This is a partial roaning pattern, often slight, usually limited to the belly, flanks, legs, tailhead, or any combination of these areas. Some geneticists suggest that all roaning in purebred Arabians is actually the action of the rabicano or sabino genes. There is scientific debate over whether roan Arabians actually exist. Unlike a true roan, a rabicano horse's body does not have intermingled white and solid hairs over the entire body, nor are the legs or head significantly darker. Another area of confusion is that some people confuse a young grey horse with a roan because of the intermixed hair colors common to both. However, a roan does not change color with age, while a gray does. There are very few Arabians registered as "roan," and fewer, if any, have been DNA tested for the roan gene.

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