Roan (color)
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Roan is a coat color found in many animals, including
Roan horses
A horse with intermixed white and colored hairs of any color is usually called a roan.
Horses with the classic or true roan pattern may be any base color which is intermingled with unpigmented white hairs on the body. Except for
- Red Roan or strawberry roan describes true or classic roan on a chestnutbase coat. The mane and tail remain red or have only a few white hairs, while the body ranges from nearly chestnut to pinkish. Geneticists prefer the term "chestnut roan," but this term is not in common use.
- Bay Roan is true roan on a bay coat. The particular shade depends on the underlying shade of bay; but the mane, tail, and lower legs are black, and the reddish body is intermingled with white hairs. The head is usually red. Formerly, bay roans were lumped together with chestnut roans and both called "red roans."
- Blue Roan is true roan on a and possess dun markings but not intermingled white hairs.
Any other coat color may also be affected by roaning. Few combinations have the same unique terminology applied to the common roan colors, although palomino roans are sometimes called honey roans.
Roan mimics
A
Roan dogs
The genetics behind roan dogs are still unclear, and at present candidate genes have been ruled out.
In dogs, roan manifests itself only in unpigmented areas, the presence and shape of which are determined by other genes.[7] This is in stark contrast to true roan horses and roan cattle, which are roan only in pigmented regions of their coat and may have white markings. Instead, dogs with roaning or ticking are born with clear, open white markings which begin to fill in with flecking in the subsequent weeks and continue to darken with age.[8] Most breed standards use the terms "ticked" and "roan" interchangeably, with the former referring to clearly defined flecks on a white background and the latter to flecks so closely spaced that the mixture appears even.[9]
The terminology that relates the underlying coat color with the roan modifier is often breed-specific, but most standards call a black dog with roaning blue. In breeds that are characterized by roaning and ticking such as the Large Munsterlander, clear white-marked individuals may be called plated.[7] The term belton is reserved for English Setters.
In 1957, Little suggested that roan and ticking were controlled separately, and postulated that roan may have been homologous to "silvered" coat in mice.
Roan cattle
Breeds of cattle known for roans are the Belgian Blue and Shorthorn. Among the former, coat color may be solid black, solid white, or blue roan; the latter may be solid red, solid white, or red roan. Belgian Blues also typically exhibit spotting patterns,[11] which are genetically separate from roan. As a result, most roan cows exhibit blotches of clearly colored and clearly white hair, with roan patches.[12] Some "cryptic" roan cattle appear solid, but upon close inspection reveal a small roan patch.[13] Roan cattle cannot "breed true" but breeding white cattle to a solid mate will always yield a roan calf. The white color typical of Charolais and White Park breeds is not related to roan.[14]
Roan in Shorthorns and Belgian Blues is controlled by the mast cell growth factor (MGF)
The reproductive condition "White Heifer Disease," associated with the MGF gene, is characterized by
Roan guinea pigs
The
About 25% of guinea pigs born to two roans are completely white, having two copies of the "roan" allele, and may have a constellation of deformities associated with "lethal white syndrome", although this condition has no relation to overo lethal white syndrome in horses or double merle syndrome in dogs. Lethal white guinea pigs ("lethals") often die shortly after birth or at weaning age, but with hand-feeding and regular dental care, lethals may live 2 to 3 years. Some lethals have reportedly lived to 6 or 7 years. It is worth noting that, unlike anophthalmic hamsters, guinea pigs with the condition are not sterile, but females may be unable to deliver live young.
Lethal white syndrome symptoms include:
- Partial or complete blindness
- Partial or complete deafness
- Microphthalmia or anophthalmia
- Unpigmentedeyes
- Missing or deformed incisors
- Deformed molars
- Elongated tooth roots
- Malabsorption in the small intestine, due in some cases to lack of intestinal villi
- Increased susceptibility to illness
Roan coloration is not to be confused with the "magpie" coloration of guinea pigs, which is a brindle color lacking red pigment due to the "chinchilla" allele, an allele also responsible for self white and silver agouti coloration.
See also
References
- ^ "roan, a. and n.1" Oxford English Dictionary. 2nd edition 1989. OED Online. Oxford University Press. 3 June 2008. <http://0-dictionary.oed.com.helin.uri.edu/cgi/entry/50207603>.
- ^ a b c d e Veterinary Genetics Laboratory. "Introduction to Coat Color Genetics". The Regents of the University of California. Retrieved 2008-06-04.
- ^ a b c "Roan Zygosity Test Information". Veterinary Genetics Laboratory Services. UC Davis. Retrieved 2009-10-01.
- S2CID 32790547.
- ^ Overton, Rebecca (2004-12-15). "In The Genes" (PDF). Quarter Horse News. American Quarter Horse Association. pp. 24–6. Archived from the original (PDF) on 2007-09-27. Retrieved 2008-06-04.
- ^ PMID 18052939.
- ^ a b Schmutz, Sheila (2007-11-12). "Spotted Patterns". Dog Coat Color Genetics. Retrieved 2008-06-04.
- ^ The Cocker Spaniel Club. "Roan". Cocker Spaniel Colours & Markings. Retrieved 2008-06-04.
- ^ ISBN 1-86307-006-0.
- ^ Clark, LA; JM Wahl; CA Rees; KE Murphy. "Retrotransposon insertion in SILV is responsible for merle patterning of the domestic dog.". Proceedings of the National Academy of Sciences of the United States of America 103. pp. 1376–81.
- PMID 17246700.
in Seitz et al. (1999)
- ^ Schmutz, Sheila (2004-02-17). "The Roan Pattern". Genetics of Coat Color Patterns in Cattle. Retrieved 2008-06-03.
- ^ S2CID 23700174.
- ^ Seitz, Schmutz, Thue & Buchanan: "Although both Charolais and White Park could be classified as white phenotypically, all typed r/r homozygous colored) at the MGF locus. Alternative loci must be responsible for these forms of white, as has been suggested previously (Olson and William 1982)."
- S2CID 18685241.
in Seitz et al. (1999)
- PMID 7682288.
- ^ Schmutz, Sheila (2004-02-13). "Conditions Associated with Coat Color". Genetics of Coat Color Patterns in Cattle. Retrieved 2008-06-03.