Roan (horse): Difference between revisions
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{{Redirect|Strawberry roan|other uses|Strawberry Roan (disambiguation)}} |
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{{for|Roan in other animals|Roan (color)}} |
{{for|Roan in other animals|Roan (color)}} |
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[[File:Red_roan_Quarter_Horse.jpg|thumb|Bay roan (sometimes called "red roan")]] |
[[File:Red_roan_Quarter_Horse.jpg|thumb|Bay roan (sometimes called "red roan")]] |
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[[File:Peruvian Paso.jpg|thumb|A |
[[File:Peruvian Paso.jpg|thumb|A "blue roan", roaning over a black base coat|alt=]] |
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[[File:Beautiful Little Roan Miniature Horse at the Kentucky Horse park (5966903656).jpg|thumb|Red roan, roaning over chestnut, sometimes called " |
[[File:Beautiful Little Roan Miniature Horse at the Kentucky Horse park (5966903656).jpg|thumb|Red roan, roaning over chestnut, sometimes called "strawberry roan"]] |
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'''Roan''' is a [[horse coat color]] pattern characterized by an even mixture of colored and white hairs on the body, while the head and "[[point coloration|points]]"—lower legs, [[Mane (horse)|mane]] and tail—are mostly solid-colored. Horses with roan coats have white hairs evenly intermingled throughout any other color. The head, legs, mane and tail have fewer scattered white hairs or none at all. The roan pattern is [[Dominance (genetics)|dominantly |
'''Roan''' is a [[horse coat color]] pattern characterized by an even mixture of colored and white hairs on the body, while the head and "[[point coloration|points]]"—lower legs, [[Mane (horse)|mane]], and tail—are mostly solid-colored. Horses with roan coats have white hairs evenly intermingled throughout any other color. The head, legs, mane, and tail have fewer scattered white hairs or none at all. The roan pattern is [[Dominance (genetics)|dominantly inherited]], and is found in many [[horse breed]]s. While the specific [[mutation]] responsible for roan has not been exactly identified, a [[DNA test]] can determine [[zygosity]] for roan in several breeds. True roan is always present at birth, though it may be hard to see until after the foal coat sheds out. The coat may lighten or darken from winter to summer, but unlike the [[Gray (horse)|gray]] coat color, which also begins with intermixed white and colored hairs, roans do not become progressively lighter in color as they age. The silvering effect of mixed white and colored hairs can create coats that look bluish or pinkish. |
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==Identification== |
==Identification== |
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Horses with the roan pattern have an even mixture of white and colored hairs in the coat.<ref name=ucdroanzyg /> These interspersed white hairs are more scattered or absent on the horse's head, mane, tail, and lower legs.<ref name=ucdroanzyg>{{cite web |url=http://www.vgl.ucdavis.edu/services/Roan.php |title=Roan Zygosity Test Information |work=Veterinary Genetics Laboratory Services |publisher=UC Davis | |
Horses with the roan pattern have an even mixture of white and colored hairs in the coat.<ref name=ucdroanzyg /> These interspersed white hairs are more scattered or absent on the horse's head, mane, tail, and lower legs.<ref name=ucdroanzyg>{{cite web |url=http://www.vgl.ucdavis.edu/services/Roan.php |title=Roan Zygosity Test Information |work=Veterinary Genetics Laboratory Services |publisher=UC Davis |access-date=2009-10-01}}</ref> The unaffected color on the legs often forms a sharp, inverted "V" above the knee and hock, not seen in other roan-like coat patterns.<ref name=NJpony>{{cite web |url=http://www.njponybreeders.org/News/articles/articles.htm |title=Articles |access-date=2009-10-06 |publisher=New Jersey Pony Breeders and Owners |url-status=dead |archive-url=https://web.archive.org/web/20091014100537/http://www.njponybreeders.org/News/articles/articles.htm |archive-date=2009-10-14 }}</ref> The nonwhite background coat may be any color, as determined by unrelated [[Equine coat color genetics|genetic factors]].<ref name=marklund2008>{{cite journal | last=Marklund | first =S |author2=M Moller |author3=K Sandberg |author4=L Andersson | year =1999 | title =Close association between sequence polymorphism in the KIT gene and the roan coat color in horses | journal =Mammalian Genome | volume =10 | pages =283–288 | doi =10.1007/s003359900987 | pmid=10051325 | issue=3 | s2cid =32790547 }}</ref> |
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Often, the background coat color is used in combination with the word "roan" to describe the shade of a roan horse's coat, such as [[Bay (horse)|bay]] roan or [[Champagne gene|gold champagne]] roan |
Often, the background coat color is used in combination with the word "roan" to describe the shade of a roan horse's coat, such as [[Bay (horse)|bay]] roan or [[Champagne gene|gold champagne]] roan,<ref name=overton>{{cite news |first=Rebecca |last=Overton |title=In The Genes |url=http://www.hancockhorses.com/article-roanQHNews.pdf |work=Quarter Horse News |publisher=American Quarter Horse Association |pages=24–6 |date=2004-12-15 |access-date=2008-06-04 |url-status=dead |archive-url=https://web.archive.org/web/20070927040626/http://www.hancockhorses.com/article-roanQHNews.pdf |archive-date=2007-09-27 }}</ref> but colloquial terms also are used for some colors. The most common terms for various roan colors are: |
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⚫ | * '''Blue roan''' is loosely applied to any roan with a dark underlying coat that gives it a bluish cast.<ref name=evans>{{cite book |title=The Horse |edition=2 |publisher=Macmillan |year=1990 |last=Evans |first=James Warren |pages=[https://archive.org/details/isbn_9780716718116/page/81 81] |chapter=Breeds in the United States |isbn=0-7167-1811-1 |quote=...blue roan comes on a dark (black, brown, or liver chestnut) background. |url-access=registration |url=https://archive.org/details/isbn_9780716718116/page/81 }}</ref> In the strictest sense, though, "blue roan" is a common synonym for a roan with a [[Black (horse)|black]] background coat.<ref name=sponenberg>{{cite book |title=Equine color genetics |last=Sponenberg |first=Dan Phillip |year=2003 |edition=2 |publisher=Wiley-Blackwell |pages=65–68 |isbn=0-8138-0759-X}}</ref> |
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⚫ | * '''Red roan''' used to include both chestnut and bay roans. In 1999, the [[American Paint Horse]] Association changed its coat color descriptions; roans with a chestnut background coat are registered "red roan", while "bay roan" is its own category.<ref name=overton2002>{{cite journal |url=http://www.painthorsejournal.com/archives/pdfs/TheWhiteStuffJan02.pdf |title=The White Stuff |journal=Paint Horse Journal |date=January 2002 |pages=106–111 |last=Overton |first=Rebecca |access-date=2009-10-06 |url-status=dead |archive-url=https://web.archive.org/web/20080807130329/http://www.painthorsejournal.com/archives/pdfs/TheWhiteStuffJan02.pdf |archive-date=2008-08-07 }}</ref> The [[American Quarter Horse]] Association followed suit in 2003.<ref name=overton /> Previously, the term '''strawberry roan''' described the pinkish color of a light chestnut or [[Sorrel (horse)|sorrel]] roan. While less common, the term '''lilac roan''' may be applied to a dark chestnut roan, and '''honey roan''' to [[palomino]]s or the lightest sorrels.<ref name=sponenberg /> |
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⚫ | * '''Blue roan''' |
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⚫ | * '''Red roan''' used to include both chestnut and bay roans. In 1999, the [[American Paint Horse]] Association changed its coat color descriptions |
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*'''Bay roan''' replaced red roan as the term for a roan with a bay background coat.<ref name=overton /> |
*'''Bay roan''' replaced red roan as the term for a roan with a bay background coat.<ref name=overton /> |
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Some roan horses have more white hair than others, and even individual horses may look lighter or darker based on the season and their coats may vary from year to year.<ref name=sponenberg /> While roan is always present at birth, the soft first coat of newborn foals may not show the white hairs well.<ref name=ucdroanzyg /> Some roan horses get darker with age.<ref name=sponenberg /> Generally, roans appear to have more white hair when they have their short summer coats and darker when they have their winter coats.<ref name=sponenberg /> These peculiar tendencies of roans led to the [[Icelandic language|Icelandic]] word for roan, which translates as "always changing color."<ref name=sponenberg /> |
Some roan horses have more white hair than others, and even individual horses may look lighter or darker based on the season, and their coats may vary from year to year.<ref name=sponenberg /> While roan is always present at birth, the soft first coat of newborn foals may not show the white hairs well.<ref name=ucdroanzyg /> Some roan horses get darker with age.<ref name=sponenberg /> Generally, roans appear to have more white hair when they have their short summer coats and darker when they have their winter coats.<ref name=sponenberg /> These peculiar tendencies of roans led to the [[Icelandic language|Icelandic]] word for roan, which translates as "always changing color."<ref name=sponenberg /> |
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⚫ | Roans have other unusual characteristics. If the skin is damaged by even a very minor scrape, cut, or [[Livestock branding|brand]], the coat grows back in solid-colored without any white hairs.<ref name=sponenberg /> These regions of solid-colored coat are called "corn spots" or "corn marks", and can appear even without the horse having had a visible injury.<ref name=sponenberg /> Another trait is reverse dappling; many horses develop rings of hair that appear slightly different-colored, called dapples, which often indicate good health. Usually dapples are darker than the surrounding coat, but on a roan, the dapples are lighter.<ref name=sponenberg /> |
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⚫ | Roans have other unusual characteristics. If the skin is damaged by even a very minor scrape, cut or [[Livestock branding|brand]], the coat grows back in solid-colored without any white hairs.<ref name=sponenberg /> These regions of solid-colored coat are called "corn spots" or "corn marks" and can appear even without the horse having had a visible injury.<ref name=sponenberg /> Another trait is reverse dappling; many horses develop rings of hair that appear slightly different-colored, called dapples, which often indicate good health. Usually dapples are darker than the surrounding coat, but on a roan, the dapples are lighter.<ref name=sponenberg /> |
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</gallery> |
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==Terminology== |
==Terminology== |
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⚫ | In the most general sense, the word "roan" refers to any animal with a mixture of white and colored hairs in the coat.<ref name=OEDroan>"''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{{Dead link|date=October 2019 |bot=InternetArchiveBot |fix-attempted=yes }}>.</ref> Recent research into [[equine coat color genetics]] indicates that "true roan" or "classic roan" is distinct from several similar patterns that are collectively called "roaning".<ref name="ucdroanzyg"/><ref name=sponenberg /> In studies of the white patterning genotypes of laboratory mice, no fewer than four produced roaning or flecking.<ref name=bennett2003>{{cite journal |last=Bennett |first=Dorothy C. |author2=M. Lynn Lamoreux |date=August 2003 |title=The Color Loci of Mice - A Genetic Century |journal=Pigment Cell Research |volume=16 |issue=4 |pages=333–344 |doi=10.1034/j.1600-0749.2003.00067.x |pmid=12859616 |s2cid=3904358 |doi-access= }}</ref> Therefore, the existence of other types of roaning conditions not covered by those mentioned here is possible and likely.<ref name=ucdroanzyg /> The patterns identified as "roaning" have particular qualities that can be used to tell them apart from true roan. |
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⚫ | In the most general sense, the word "roan" refers to any animal with a mixture of white and colored hairs in the coat.<ref name=OEDroan>"''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{{Dead link|date=October 2019 |bot=InternetArchiveBot |fix-attempted=yes }}>.</ref> Recent research into [[equine coat color genetics]] indicates that "true roan" or "classic roan" is distinct from several similar patterns |
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==Roan mimics== |
==Roan mimics== |
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===Gray vs. roan=== |
===Gray vs. roan=== |
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[[File:Nokota Horses.jpg|thumb|Blue roans, such as these may be confused with young gray horses or blue duns]] |
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{{Main|Gray (horse)}} |
{{Main|Gray (horse)}} |
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⚫ | Roans are sometimes mistaken for [[Gray (horse)|grays]]. However, grays lighten with age, while roans do not. Gray is one of the most common coat colors found in horses, and is found in almost all breeds. The defining characteristic of the gray coat is that it becomes progressively lighter over time.<ref name=locke2002>{{cite journal |last=Locke |first=MM |author2=MCT Penedo |author3=SJ Brickker |author4=LV Millon |author5=JD Murray |title=Linkage of the grey coat colour locus to microsatellites on horse chromosome 25 |journal=Animal Genetics |volume=33 |year=2002 |pages=329–337 |quote=The progressive loss of colour in the hair of grey horses is controlled by a dominantly inherited allele at the Grey locus (G^G). Foals are born any colour depending on the alleles present at other colour determining loci. |doi=10.1046/j.1365-2052.2002.00885.x |pmid=12354140 |issue=5}}</ref> Gray [[foal]]s may be born any color, and there may be no indication of the future gray coat at birth.<ref name=bowling57>{{cite book | |
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⚫ | Roans are sometimes mistaken for [[Gray (horse)|grays]]. However, grays lighten with age, while roans do not. Gray is one of the most common coat colors found in horses, and is found in almost all breeds. The defining characteristic of the gray coat is that it becomes progressively lighter over time.<ref name=locke2002>{{cite journal |last=Locke |first=MM |author2=MCT Penedo |author3=SJ Brickker |author4=LV Millon |author5=JD Murray |title=Linkage of the grey coat colour locus to microsatellites on horse chromosome 25 |journal=Animal Genetics |volume=33 |year=2002 |pages=329–337 |quote=The progressive loss of colour in the hair of grey horses is controlled by a dominantly inherited allele at the Grey locus (G^G). Foals are born any colour depending on the alleles present at other colour determining loci. |doi=10.1046/j.1365-2052.2002.00885.x |pmid=12354140 |issue=5}}</ref> Gray [[foal]]s may be born any color, and there may be no indication of the future gray coat at birth.<ref name=bowling57>{{cite book |last1=Bowling |first1=Ann T. |last2=Ruvinsky |first2=Anatoly |title=The genetics of the horse |url=https://archive.org/details/geneticshorsecab00bowl |url-access=limited |page=[https://archive.org/details/geneticshorsecab00bowl/page/n329 57] |year=2000 |publisher=CABI |isbn=0-85199-429-6}}</ref> Mature grays may retain none of their original coat color, and have a "[[White (horse)|white]]" coat, while the color of the skin and [[Equine vision|eyes]] is unchanged. The first white hairs are usually seen around the muzzle and eyes.<ref name=bowling57/> As a gray may go from entirely colored to entirely white over the course of its life, the process of "graying out" can, at times, closely resemble roan.<ref name=UCDint>{{cite web |url=http://www.vgl.ucdavis.edu/services/coatcolor.php |title=Introduction to Coat Color Genetics|author=Veterinary Genetics Laboratory |access-date=2008-06-04 |publisher=The Regents of the University of California }}</ref> [[Thoroughbred]] and [[Arabian Horse]]s registered as "roan" are often gray, especially [[chestnut (coat)|chestnuts]] turning gray.<ref name=bowling57/> Unlike grays, roans do not develop more white hair with age, and without white markings, roans retain colored heads. |
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{{Main|Grullo|Dun gene}} |
{{Main|Grullo|Dun gene}} |
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Blue dun or [[grullo]] (also grulla, mouse dun) coloring is created by the [[dun gene]] acting on a [[black (horse)|black]] base coat, is a coat color with a bluish cast and darker points.<ref name=sponenberggrullo>Sponenberg, Dan Phillip (2003). "Grullo is the Spanish name for the crane bird, and these horses are similar to the bluish color of the sandhill crane." |
Blue dun or [[grullo]] (also grulla, mouse dun) coloring is created by the [[dun gene]] acting on a [[black (horse)|black]] base coat, and is a coat color with a bluish cast and darker points.<ref name=sponenberggrullo>Sponenberg, Dan Phillip (2003). "''Grullo'' is the Spanish name for the crane bird, and these horses are similar to the bluish color of the sandhill crane." p. 37.</ref> Unlike blue roans, grullos are solid color and appear bluish due to low amounts of [[Melanin|pigment]] in each hair, not interspersed white hairs.<ref name=UCDVGLDUN>{{cite web |url=http://www.vgl.ucdavis.edu/services/dunhorse.php |title=Dun Zygosity Test |publisher=UC Davis Veterinary Genetics Laboratory |access-date=2009-05-27}}</ref> Like other dun coat colors, grullos have dark or black [[primitive markings]], always including a stripe down the back.<ref name=UCDVGLDUN /> |
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===Rabicano vs. roan=== |
===Rabicano vs. roan=== |
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{{Main|Rabicano}} |
{{Main|Rabicano}} |
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[[File:Dancingcolors.jpg|thumb|right|An extensively expressed [[rabicano]] [[Arabian horse]] |
[[File:Dancingcolors.jpg|thumb|right|An extensively expressed [[rabicano]] [[Arabian horse]]]] |
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[[File:New forest pony3 june 2013.JPG|thumb|A bay roan that also has bay rabicano features evidenced by the light hairs in its mane and base of tail]] |
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One pattern of roaning is [[rabicano]], also called white ticking.<ref name=sponenbergrabicano>{{cite book |title=Equine color genetics |last=Sponenberg |first=Dan Phillip |year=2003 |edition=2 |publisher=Wiley-Blackwell |pages=69 |chapter=4 / Patterns of White Occurring on Base Colors |isbn=0-8138-0759-X}}</ref> While true roans have an even intermixture of white hairs throughout the body, except the extremities, the white hairs of a rabicano are densest around the base of the tail and the flank.<ref name=sponenberg /> Rabicano roaning frequently forms rings of white hair around the base of the tail, and in extensively roaned rabicanos, the white hairs may converge to form vertical stripes over the ribcage.<ref name=sponenberg /> Rabicano is found in many breeds, and may account for some "roan" [[Arabian horse|Arabians]].<ref name=sponenberg /> |
One pattern of roaning is [[rabicano]], also called white ticking.<ref name=sponenbergrabicano>{{cite book |title=Equine color genetics |last=Sponenberg |first=Dan Phillip |year=2003 |edition=2 |publisher=Wiley-Blackwell |pages=69 |chapter=4 / Patterns of White Occurring on Base Colors |isbn=0-8138-0759-X}}</ref> While true roans have an even intermixture of white hairs throughout the body, except the extremities, the white hairs of a rabicano are densest around the base of the tail and the flank.<ref name=sponenberg /> Rabicano roaning frequently forms rings of white hair around the base of the tail, and in extensively roaned rabicanos, the white hairs may converge to form vertical stripes over the ribcage.<ref name=sponenberg /> Rabicano is found in many breeds, and may account for some "roan" [[Arabian horse|Arabians]].<ref name=sponenberg /> |
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===Sabino vs. roan=== |
===Sabino vs. roan=== |
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{{main|Sabino horse}} |
{{main|Sabino horse}} |
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⚫ | Roaning is also associated with some of the [[Sabino horse|sabino]] white spotting patterns.<ref name=overton /> |
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⚫ | Roaning is also associated with some of the [[Sabino horse|sabino]] white spotting patterns.<ref name=overton /> Many patterns in many breeds are called "sabino", and these patterns usually feature irregular, rough-edged patches of white that originate from the lower legs, face, and ventral midline.<ref name=brooks2005>{{cite journal |doi=10.1007/s00335-005-2472-y |pmid=16284805 |title=Exon skipping in the KIT gene causes a Sabino spotting pattern in horses |journal=Mammalian Genome |volume=16 |issue=11 |pages=893–902 |year=2005 |last1=Brooks |first1=Samantha A. |last2=Bailey |first2=Ernest |s2cid=32782072 }}</ref> The borders of these white patches can be heavily roaned, and some sabinos can be mistaken for roans.<ref name=overton /> The roaning of sabinos originates in a white patch, and the roaning is uneven.<ref name=overton /> |
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===Varnish roan vs. roan=== |
===Varnish roan vs. roan=== |
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{{Main|Varnish roan}} |
{{Main|Varnish roan}} |
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⚫ | The [[leopard complex]] colors, characteristic of the [[Appaloosa]] breed, have several manifestations that feature mixtures of white and colored hairs. A [[varnish roan]], one type of leopard complex coat color also called "marble", is an all-over blend of white and colored hairs.<ref name=sponenbergvarnish>{{cite book |title=Equine color genetics |last=Sponenberg |first=Dan Phillip |year=2003 |edition=2 |publisher=Wiley-Blackwell |pages=91 |chapter=5 / Patterns Characterized by Patches of White |isbn=0-8138-0759-X}}</ref> Patches of skin that lie close to the bone, such as on the face and legs, and the point of shoulder and point of hip, do not grow as much white hair. These darker patches are called "varnish marks" and are not found in true roans.<ref name=sponenbergvarnish /> Varnish roans can also be distinguished from true roans by the presence of leopard complex characteristics, such as the white [[sclera]], finely striped [[horse hoof|hooves]], and [[mottling|mottled]] skin around the eyes, muzzle, and genitals.<ref name=sponenbergvarnish /> |
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⚫ | The [[leopard complex]] colors, characteristic of the [[Appaloosa]] breed, have several manifestations that feature mixtures of white and colored hairs. A [[varnish roan]], one type of leopard complex coat color also called "marble", is an all-over blend of white and colored hairs.<ref name=sponenbergvarnish>{{cite book |title=Equine color genetics |last=Sponenberg |first=Dan Phillip |year=2003 |edition=2 |publisher=Wiley-Blackwell |pages=91 |chapter=5 / Patterns Characterized by Patches of White |isbn=0-8138-0759-X}}</ref> Patches of skin that lie close to the bone, such as on the face and legs, and the point of shoulder and point of hip, do not grow as much white hair. These darker patches are called "varnish marks" and are not found in true roans.<ref name=sponenbergvarnish /> Varnish roans can also be distinguished from true roans by the presence of leopard complex characteristics, such as the white [[sclera]], finely striped [[horse hoof|hooves]], and [[mottling|mottled]] skin around the eyes, muzzle, and genitals.<ref name=sponenbergvarnish /> |
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==Prevalence== |
==Prevalence== |
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True or classic roan is common in European [[Draft horse|draft]] breeds such as the [[Belgian |
True or classic roan is common in European [[Draft horse|draft]] breeds such as the [[Belgian Draught|Brabant]], [[Ardennes (horse)|Ardennes]], [[Trait Du Nord]], [[Italian Heavy Draft]], and [[Rhenish-German Cold-Blood]].<ref name=sponenberg /> It is also found regularly in North American breeds such as the [[American Quarter Horse|Quarter Horse]], [[American Paint Horse|Paint Horse]], [[Peruvian Paso]], [[Paso Fino]], [[Standardbred]], [[Spanish Mustang]], [[Missouri Fox Trotter]] and [[Tennessee Walking Horse]].<ref name=ucdroanzyg /><ref name=sponenberg /><ref name=bowling64>{{cite book |last1=Bowling |first1=Ann T. |last2=Ruvinsky |first2=Anatoly |title=The genetics of the horse |url=https://archive.org/details/geneticshorse00bowl |url-access=limited |pages=[https://archive.org/details/geneticshorse00bowl/page/n63 64]–5 |year=2000 |publisher=CABI |isbn=0-85199-429-6}}</ref><ref name=twhbea>{{cite web |url=http://www.twhbea.com/breed/modifiers.php |title=Coat Color: Modifiers |work=The Tennessee Walking Horse Breed |publisher=Tennessee Walking Horse Breeders' and Exhibitors' Association |access-date=2009-10-01 |url-status=dead |archive-url=https://web.archive.org/web/20110717115741/http://www.twhbea.com/breed/modifiers.php |archive-date=2011-07-17 }}</ref> |
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British ponies such as [[Dales Pony|Dales |
British ponies such as [[Dales Pony|Dales]], [[Welsh Pony|Welsh]], [[Gypsy Vanner horse|Gypsy Cob]], [[Shetland pony|Shetland]], [[Connemara Pony|Connemara]], and [[New Forest Pony|New Forest]] ponies may be roan. [[Icelandic Horse]]s and [[Miniature Horse]]s may also be roan.<ref name=ucdroanzyg /><ref name=sponenberg /> Some roan [[Trakehner]]s and [[American Saddlebred]]s are known.<ref name=ASHA>{{cite web |url=https://www.asha.net/html/files/conformation_brochure.pdf |title=Conformation Brochure |publisher=American Saddlebred Horse Association |access-date=2009-10-01 |url-status=dead |archive-url=https://web.archive.org/web/20110723020924/https://www.asha.net/html/files/conformation_brochure.pdf |archive-date=2011-07-23 }}</ref> The [[Hokkaido Pony]] of [[Japan]] may also be roan.<ref name=overton-breeds>Overton, Rebecca (2004). "Other studies discovered them in two other equine breeds, the Ardennais, found in France, and the Hokkaido, which live in Japan."</ref> |
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To date, only one Thoroughbred family has been genetically verified as true roan, and there are no [[Arabian horse|Arabians]] that are true roan.<ref name=peters>{{cite news |first=Anne |last=Peters |title=A roan by any other name is a roan |url=http://www.thoroughbredtimes.com/weekly-feature-articles/2002/May/04/A-roan-by-any-other-name-is-a-roan.aspx |work=Thoroughbred Times |publisher=Thoroughbred Times Co. Inc. |location=Lexington |date=2002-05-04 |access-date=2008-06-04 |archive-date=2010-02-28 |archive-url=https://web.archive.org/web/20100228063910/http://www.thoroughbredtimes.com/weekly-feature-articles/2002/May/04/A-roan-by-any-other-name-is-a-roan.aspx |url-status=dead }}</ref> A small number of [[Thoroughbred]] offspring of the [[brindle]]-patterned stallion Catch A Bird phenotypically appear to be true roan, and though few of those reproduced, some offspring of his daughter Slip Catch, though registered as bay, have apparently been verified as carrying the roan gene.<ref>{{cite web|url=http://www.whitehorseproductions.com/tbcolor_roan.html|title=(Phenotypically) True Roan Thoroughbreds: A New Mutation|access-date=Nov 18, 2021}}</ref> <ref>{{cite web |title=2021 AUGUST (Late) Online Sale {{!}} Inglis Digital Online Auctions |url=https://inglisdigital.com/results/30000119.100.htm |website=inglisdigital.com |access-date=20 November 2021}}</ref> |
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Nonetheless, most Thoroughbreds and Arabians with roan-like coats are most likely related to graying or [[rabicano]] characteristics.<ref name=JC>{{cite web |url=http://www.jockeyclub.com/registry.asp?section=3#color |title=Section IV: Color Guide |access-date=2009-10-01 |publisher=The Jockey Club |work=The American Stud Book Principal Rules and Requirements}}</ref><ref name=AHA>{{cite web |url=http://www.arabianhorses.org/registration/Markings/Color.asp |title=What color is my horse? |work=Purebred Registration |publisher=Arabian Horse Association |access-date=2009-10-01 |url-status=dead |archive-url=https://web.archive.org/web/20080514145158/http://www.arabianhorses.org/registration/markings/Color.asp |archive-date=2008-05-14 }}</ref> Thoroughbred "roans" are described by the [[Jockey Club]] as a mixture of white with red or brown hairs, but which researchers identify as chestnuts turning gray.<ref name=bowling57/><ref name=JC /> The Arabian Horse Association defines "roan" as an even mixture of white and colored, usually chestnut, hairs, but researchers suggest most animals so classified are probably either rabicano, or have a partially-spotted pattern that results from a [[dominant white]] allele.<ref name=bowling57 /><ref name="AHA"/> |
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⚫ | |||
==Genetics== |
==Genetics== |
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{{see also|Equine coat color genetics|Introduction to genetics}} |
{{see also|Equine coat color genetics|Introduction to genetics}} |
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Roan is a simple [[Dominance relationship|dominant]] trait symbolized by the ''Rn'' [[allele]].<ref name=ucdroanzyg /> Traits that are dominantly |
Roan is a simple [[Dominance relationship|dominant]] trait symbolized by the ''Rn'' [[allele]].<ref name=ucdroanzyg /> Traits that are dominantly inherited cannot skip generations, meaning that two nonroan parents cannot produce a roan offspring.<ref name=overton /> In cases where roan has appeared to skip generations, one of the parents is usually discovered to be slightly roaned.<ref name=sponenberg /> A roan can also be born from two seemingly nonroan parents if the roan coat is "masked" by extensive white markings or gray.<ref name=overton /> In some cases, the supposedly roan offspring is not true roan at all, but rabicano, sabino, or influenced by some other genetic factor. |
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The [[University of California, Davis]] [[University of California, Davis School of Veterinary Medicine|School of Veterinary Medicine]]'s genetics services |
The [[University of California, Davis]] [[University of California, Davis School of Veterinary Medicine|School of Veterinary Medicine]]'s genetics services has developed a [[DNA test]] that uses [[genetic marker]]s to indirectly determine the number of ''Rn'' or ''rn'' alleles a horse has.<ref name=ucdroanzyg /> The [[mutation]] responsible for true roan has not yet been identified exactly, but been assigned to equine [[chromosome]] 3 (ECA3) in the KIT sequence.<ref name=marklund2008/> A roan zygosity test is reliable for American Quarter Horse, American Paint Horse, Welsh Pony, and Gypsy Cob.<ref name=ucdroanzyg /> Until a direct test is developed, the roan zygosity test may enable breeders to produce roans more reliably. |
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===Homozygous roan=== |
===Homozygous roan=== |
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A 1979 study of American-bred [[Belgian |
A 1979 study of American-bred [[American Belgian Draft|Belgian draft horses]] found fewer roan offspring from roan-to-roan matings than expected for a [[Dominance (genetics)|simple dominant]] trait. Finding neither stillborn nor sickly, short-lived foals from these roan parents, the researchers concluded that in the [[Zygosity|homozygous]] condition the roan gene was lethal to the [[embryo]] or [[fetus]].<ref name=hintz1979>{{cite journal |title=Lethal dominant roan in horses |last1=Hintz |last2=van Vleck |journal=Journal of Heredity |year=1979 |volume=70 |issue=2 |pages=145–6|doi=10.1093/oxfordjournals.jhered.a109213 }}</ref> Other studies at the time were using progeny ratios to identify potential lethality related to other coat colors, such as "[[dominant white]]" and "[[Lethal white syndrome|lethal white]]", so roan was believed to follow a similar pattern.<ref name=hintz1979 /> Genetic science in the 1970s could not provide a clear answer, as methods of [[Genetic analysis|molecular analysis]] had not yet been developed.<ref name=overton-penedo>"The paper by Hintz and Van Vleck caused all this commotion, but there were earlier mentions of a roan cross being lethal, too," Penedo explained. "But it was never fully established by any molecular analysis that homozygous roan horses would not be produced from matings of two roan parents." in Overton, 2004.</ref> |
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The belief in "lethal roan" persisted until recently, when homozygous roan stallions with large numbers of offspring - all roan - were satisfactorily identified.<ref name=ucdroanzyg /> Homozygous roan stallions were identified in both European populations of Belgian horses in 1977, and in North American, in |
The belief in "lethal roan" persisted until recently, when homozygous roan stallions with large numbers of offspring - all roan - were satisfactorily identified.<ref name=ucdroanzyg /> Homozygous roan stallions were identified in both European populations of Belgian horses in 1977, and in North American, in Quarter Horse stallions.<ref name=bowling57 /><ref name=HZroans>{{cite web |url=http://www.hancockhorses.com/homoz-roan.html |title=Homozygous Roans |access-date=2008-06-04 |publisher=Hancock Horses}}</ref> |
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In some breeds, homozygous roans can be identified by an indirect [[genetic marker|DNA marker]] test.<ref name=ucdroanzyg /> Such horses, with the [[genotype]] ''Rn/Rn'', produce 100% roan offspring.<ref name=ucdroanzyg /> Homozygous roans and heterozygous roans (''Rn/rn'') are identical in appearance.<ref name=sponenberg /> |
In some breeds, homozygous roans can be identified by an indirect [[genetic marker|DNA marker]] test.<ref name=ucdroanzyg /> Such horses, with the [[genotype]] ''Rn/Rn'', produce 100% roan offspring.<ref name=ucdroanzyg /> Homozygous roans and heterozygous roans (''Rn/rn'') are identical in appearance.<ref name=sponenberg /> |
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===Equine linkage group II=== |
===Equine linkage group II=== |
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{{see also|Genetic linkage}} |
{{see also|Genetic linkage}} |
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During the production of [[sex cells]], |
During the production of [[sex cells]], DNA is "reshuffled" to ensure that the next generation does not inherit ancestral [[chromosome]]s as is, but a mixture of DNA from each parent. Paired chromosomes exchange parallel pieces of DNA, a process called [[chromosomal crossover]], prior to being passed on to the next generation. When particular [[gene]]s are located physically close together on a chromosome, they tend to be exchanged together. The rate at which two genes are passed on together can be used to calculate their [[Centimorgan|distance]] from each other on the chromosome. Genes that tend to be passed on as a group form what is called a "[[Genetic linkage|linkage group]]". |
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⚫ | Equine linkage group II includes a number of genes. The first linkage was found between a [[blood type]] [[Genetic marker|marker]] and [[tobiano]] white spotting in 1978.<ref name=smith>{{cite journal |last=Trommerhausen-Smith |first=Ann |title=Linkage of tobiano coat spotting and albumin markers in a pony family |journal=Journal of Heredity |year=1978 |volume=69 |issue=4 |pages=214–216 |publisher=American Genetic Association |pmid=569673|doi=10.1093/oxfordjournals.jhered.a108933 }}</ref> The same blood type marker, [[albumin]], was linked to another blood protein called [[vitamin D-binding protein]].<ref name=sandberg1978>{{cite journal |title=Close linkage between the albumin and Gc loci in the horse |last1=Sandberg |first1=Kaj |last2=Juneja |first2=R. Kumar |doi=10.1111/j.1365-2052.1978.tb01430.x |pmid=751533 |journal=Animal Genetics |volume=9 |year=2009 |issue=3 |pages=169–173}}</ref> In 1982, a linkage grouping was proposed, including three genes for [[Serum (blood)|serum]] [[protein]]s, and three for [[Equine coat color|coat color]]: tobiano spotting, [[Chestnut (coat)|chestnut]], and roan.<ref name=andersson1982>{{cite journal |last1=Andersson |first1=L |last2=Sandberg |first2=K |journal=Journal of Heredity |date=Mar–Apr 1982 |volume=73 |issue=2 |pages=91–4 |title=A linkage group composed of three coat color genes and three serum protein loci in horses |pmid=7096983}}</ref> Research since equine linkage group II was defined has identified the exact location of the tobiano allele and the chestnut allele.<ref name=haase>{{cite journal |title=An equine chromosome 3 inversion is associated with the tobiano spotting pattern in German horse breeds |last=Haase |first=B |author2=Jude R |author3=Brooks SA |author4=Leeb T |journal=Animal Genetics |volume=39 |issue=3 |pages=306–309 |date=June 2008 |doi=10.1111/j.1365-2052.2008.01715.x |pmid=18410476}}</ref><ref name=marklund1996>{{cite journal |last=Marklund |first=L |author2=Moller MJ |author3=Sandberg K |author4=Andersson L |date=Dec 1996 |title=A missense mutation in the gene for melanocyte-stimulating hormone receptor (MC1R) is associated with the chestnut coat color in horses |journal=Mammalian Genome |volume=7 |issue=12 |pages=895–9 |doi=10.1007/s003359900264 |pmid=8995760|s2cid=29095360 }}</ref> The region of the chromosome that harbors the roan gene is [[Homology (biology)|homologous]] to parts of chromosomes in other species that also control coat color, even some similar to roan.<ref name=marklund2008/> Presently, the ''[[CD117|KIT]]'' gene is the primary candidate gene for roan.<ref name=marklund2008/> While a [[chromosomal inversion]] of ''KIT'' causes [[tobiano]] white spotting, ''KIT'' also harbors one or more [[allele]]s responsible for [[Sabino horse|sabino]] spotting, no fewer than eleven alleles responsible for [[dominant white]] spotting, and is thought to be a major contributor to many other forms of less distinctive [[Horse markings|white markings]].<ref name=brooks2005/><ref name=haase2007>{{cite journal|vauthors=Haase B, Brooks SA, Schlumbaum A, Azor PJ, Bailey E, etal |year=2007 |title=Allelic Heterogeneity at the Equine KIT Locus in Dominant White (W) Horses |journal=PLOS Genet |volume=3 |issue=11|pages= e195 |doi=10.1371/journal.pgen.0030195| pmid=17997609| pmc=2065884 |doi-access=free }}</ref><ref name=haase2009>{{cite journal |title=Seven novel KIT mutations in horses with white coat colour phenotypes |doi=10.1111/j.1365-2052.2009.01893.x |journal =Animal Genetics |year=2009|last=Haase |first=B |author2=SA Brooks |author3=T Tozaki |author4=D Burger |author5=P-A Poncet |author6=S Rieder |author7=T Hasegawa |author8=C Penedo |author9=T Leeb |pmid=19456317 |volume=40 |issue=5 |pages=623–9}}</ref><ref name=rieder2008>{{cite journal |title=Genetic Analysis of White Facial and Leg Markings in the Swiss Franches-Montagnes Horse Breed |last=Rieder |first=Stefan |author2=Christian Hagger |author3=Gabriela Obexer-Ruff |author4=Tosso Leeb |author5=Pierre-André Poncet |journal=Journal of Heredity |publisher=The American Genetic Association |doi=10.1093/jhered/esm115 |date=2008-02-21 |quote=Our association analysis indicated that the putative major gene for white markings is located at or near the KIT locus |pmid=18296388 |volume=99 |issue=2 |pages=130–6|doi-access=free }}</ref> |
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⚫ | |||
⚫ | Equine linkage group II includes a number of genes. The first linkage was found between a [[blood type]] [[Genetic marker|marker]] and [[tobiano]] white spotting in 1978.<ref name=smith>{{cite journal |last=Trommerhausen-Smith |first=Ann |title=Linkage of tobiano coat spotting and albumin markers in a pony family |journal=Journal of Heredity |year=1978 |volume=69 |issue=4 |pages=214–216 |publisher=American Genetic Association |pmid=569673|doi=10.1093/oxfordjournals.jhered.a108933 }}</ref> The same blood type marker, [[albumin]], was linked to another blood protein called [[vitamin D-binding protein]].<ref name=sandberg1978>{{cite journal |title=Close linkage between the albumin and Gc loci in the horse | |
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The effect of linkage between roan and chestnut is readily observed. If a horse possesses one chromosome with the [[wildtype]] |
The effect of linkage between roan and chestnut is readily observed. If a horse possesses one chromosome with the [[wildtype]] nonchestnut allele and the dominant roan allele (''E'' and ''Rn''), while the other chromosome contains the recessive chestnut allele and the recessive nonroan allele (''e'' and ''rn''), it will outwardly appear blue roan, barring the influence of other genes. Normally, the chestnut and roan alleles would be separated during chromosomal crossover, but these two linked genes usually remain together. Such a horse will produce sex cells that are either ''E/Rn'' or ''e/rn''. Mated to chestnut nonroan partners (''e/rn''), the horse would produce primarily blue roans, or chestnut nonroans, but few chestnut roans and few black nonroans.<ref name=overton /> If the recessive ''e'' and dominant ''Rn'' were on the same chromosome, though, the horse would be expected to produce primarily chestnut roans and nonchestnut nonroans with chestnut, nonroan partners. |
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{{Clear}} |
{{Clear}} |
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===Cultural/Historical References=== |
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The Blue Roan was a popular horse kept and ridden by the 10th Sikh Guru, [[Guru Gobind Singh]] during the late 17th-early 18th century. He was known as the "Blue Horse Rider" or "One Who Rides the Blue Horse" during his time.{{cn|date=February 2023}} |
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== See also == |
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* [[Strawberry roan (horse color)]] |
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* [[Chestnut (horse color)]] |
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==References== |
==References== |
Latest revision as of 22:47, 31 March 2024
Roan is a horse coat color pattern characterized by an even mixture of colored and white hairs on the body, while the head and "points"—lower legs, mane, and tail—are mostly solid-colored. Horses with roan coats have white hairs evenly intermingled throughout any other color. The head, legs, mane, and tail have fewer scattered white hairs or none at all. The roan pattern is dominantly inherited, and is found in many horse breeds. While the specific mutation responsible for roan has not been exactly identified, a DNA test can determine zygosity for roan in several breeds. True roan is always present at birth, though it may be hard to see until after the foal coat sheds out. The coat may lighten or darken from winter to summer, but unlike the gray coat color, which also begins with intermixed white and colored hairs, roans do not become progressively lighter in color as they age. The silvering effect of mixed white and colored hairs can create coats that look bluish or pinkish.
Identification
[edit]Horses with the roan pattern have an even mixture of white and colored hairs in the coat.[1] These interspersed white hairs are more scattered or absent on the horse's head, mane, tail, and lower legs.[1] The unaffected color on the legs often forms a sharp, inverted "V" above the knee and hock, not seen in other roan-like coat patterns.[2] The nonwhite background coat may be any color, as determined by unrelated genetic factors.[3]
Often, the background coat color is used in combination with the word "roan" to describe the shade of a roan horse's coat, such as bay roan or gold champagne roan,[4] but colloquial terms also are used for some colors. The most common terms for various roan colors are:
- Blue roan is loosely applied to any roan with a dark underlying coat that gives it a bluish cast.[5] In the strictest sense, though, "blue roan" is a common synonym for a roan with a black background coat.[6]
- Red roan used to include both chestnut and bay roans. In 1999, the American Paint Horse Association changed its coat color descriptions; roans with a chestnut background coat are registered "red roan", while "bay roan" is its own category.[7] The American Quarter Horse Association followed suit in 2003.[4] Previously, the term strawberry roan described the pinkish color of a light chestnut or sorrel roan. While less common, the term lilac roan may be applied to a dark chestnut roan, and honey roan to palominos or the lightest sorrels.[6]
- Bay roan replaced red roan as the term for a roan with a bay background coat.[4]
Some roan horses have more white hair than others, and even individual horses may look lighter or darker based on the season, and their coats may vary from year to year.[6] While roan is always present at birth, the soft first coat of newborn foals may not show the white hairs well.[1] Some roan horses get darker with age.[6] Generally, roans appear to have more white hair when they have their short summer coats and darker when they have their winter coats.[6] These peculiar tendencies of roans led to the Icelandic word for roan, which translates as "always changing color."[6]
Roans have other unusual characteristics. If the skin is damaged by even a very minor scrape, cut, or brand, the coat grows back in solid-colored without any white hairs.[6] These regions of solid-colored coat are called "corn spots" or "corn marks", and can appear even without the horse having had a visible injury.[6] Another trait is reverse dappling; many horses develop rings of hair that appear slightly different-colored, called dapples, which often indicate good health. Usually dapples are darker than the surrounding coat, but on a roan, the dapples are lighter.[6]
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Corn marks or corn spots occur where a roan's skin has been damaged. The hair grows back in without any white.
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The forelegs of this bay roan show the characteristic inverted "V" of dark hair not affected by roan.
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This strawberry roan mare, though very light-colored, is still identifiable as a roan by the dark color of her extremities and the brand on her hindquarters, which has grown back in without white hairs.
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Reverse dapples on a bay roan
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This dark bay roan, painted in the 18th century carrying the Duke of Württemberg, has dark extremities and corn spots.
Terminology
[edit]In the most general sense, the word "roan" refers to any animal with a mixture of white and colored hairs in the coat.[8] Recent research into equine coat color genetics indicates that "true roan" or "classic roan" is distinct from several similar patterns that are collectively called "roaning".[1][6] In studies of the white patterning genotypes of laboratory mice, no fewer than four produced roaning or flecking.[9] Therefore, the existence of other types of roaning conditions not covered by those mentioned here is possible and likely.[1] The patterns identified as "roaning" have particular qualities that can be used to tell them apart from true roan.
Roan mimics
[edit]Gray vs. roan
[edit]Roans are sometimes mistaken for grays. However, grays lighten with age, while roans do not. Gray is one of the most common coat colors found in horses, and is found in almost all breeds. The defining characteristic of the gray coat is that it becomes progressively lighter over time.[10] Gray foals may be born any color, and there may be no indication of the future gray coat at birth.[11] Mature grays may retain none of their original coat color, and have a "white" coat, while the color of the skin and eyes is unchanged. The first white hairs are usually seen around the muzzle and eyes.[11] As a gray may go from entirely colored to entirely white over the course of its life, the process of "graying out" can, at times, closely resemble roan.[12] Thoroughbred and Arabian Horses registered as "roan" are often gray, especially chestnuts turning gray.[11] Unlike grays, roans do not develop more white hair with age, and without white markings, roans retain colored heads.
Dun vs. roan
[edit]Blue dun or grullo (also grulla, mouse dun) coloring is created by the dun gene acting on a black base coat, and is a coat color with a bluish cast and darker points.[13] Unlike blue roans, grullos are solid color and appear bluish due to low amounts of pigment in each hair, not interspersed white hairs.[14] Like other dun coat colors, grullos have dark or black primitive markings, always including a stripe down the back.[14]
Rabicano vs. roan
[edit]One pattern of roaning is rabicano, also called white ticking.[15] While true roans have an even intermixture of white hairs throughout the body, except the extremities, the white hairs of a rabicano are densest around the base of the tail and the flank.[6] Rabicano roaning frequently forms rings of white hair around the base of the tail, and in extensively roaned rabicanos, the white hairs may converge to form vertical stripes over the ribcage.[6] Rabicano is found in many breeds, and may account for some "roan" Arabians.[6]
Sabino vs. roan
[edit]Roaning is also associated with some of the sabino white spotting patterns.[4] Many patterns in many breeds are called "sabino", and these patterns usually feature irregular, rough-edged patches of white that originate from the lower legs, face, and ventral midline.[16] The borders of these white patches can be heavily roaned, and some sabinos can be mistaken for roans.[4] The roaning of sabinos originates in a white patch, and the roaning is uneven.[4]
Varnish roan vs. roan
[edit]The leopard complex colors, characteristic of the Appaloosa breed, have several manifestations that feature mixtures of white and colored hairs. A varnish roan, one type of leopard complex coat color also called "marble", is an all-over blend of white and colored hairs.[17] Patches of skin that lie close to the bone, such as on the face and legs, and the point of shoulder and point of hip, do not grow as much white hair. These darker patches are called "varnish marks" and are not found in true roans.[17] Varnish roans can also be distinguished from true roans by the presence of leopard complex characteristics, such as the white sclera, finely striped hooves, and mottled skin around the eyes, muzzle, and genitals.[17]
Prevalence
[edit]True or classic roan is common in European draft breeds such as the Brabant, Ardennes, Trait Du Nord, Italian Heavy Draft, and Rhenish-German Cold-Blood.[6] It is also found regularly in North American breeds such as the Quarter Horse, Paint Horse, Peruvian Paso, Paso Fino, Standardbred, Spanish Mustang, Missouri Fox Trotter and Tennessee Walking Horse.[1][6][18][19]
British ponies such as Dales, Welsh, Gypsy Cob, Shetland, Connemara, and New Forest ponies may be roan. Icelandic Horses and Miniature Horses may also be roan.[1][6] Some roan Trakehners and American Saddlebreds are known.[20] The Hokkaido Pony of Japan may also be roan.[21]
To date, only one Thoroughbred family has been genetically verified as true roan, and there are no Arabians that are true roan.[22] A small number of Thoroughbred offspring of the brindle-patterned stallion Catch A Bird phenotypically appear to be true roan, and though few of those reproduced, some offspring of his daughter Slip Catch, though registered as bay, have apparently been verified as carrying the roan gene.[23] [24]
Nonetheless, most Thoroughbreds and Arabians with roan-like coats are most likely related to graying or rabicano characteristics.[25][26] Thoroughbred "roans" are described by the Jockey Club as a mixture of white with red or brown hairs, but which researchers identify as chestnuts turning gray.[11][25] The Arabian Horse Association defines "roan" as an even mixture of white and colored, usually chestnut, hairs, but researchers suggest most animals so classified are probably either rabicano, or have a partially-spotted pattern that results from a dominant white allele.[11][26]
Genetics
[edit]Roan is a simple dominant trait symbolized by the Rn allele.[1] Traits that are dominantly inherited cannot skip generations, meaning that two nonroan parents cannot produce a roan offspring.[4] In cases where roan has appeared to skip generations, one of the parents is usually discovered to be slightly roaned.[6] A roan can also be born from two seemingly nonroan parents if the roan coat is "masked" by extensive white markings or gray.[4] In some cases, the supposedly roan offspring is not true roan at all, but rabicano, sabino, or influenced by some other genetic factor.
The University of California, Davis School of Veterinary Medicine's genetics services has developed a DNA test that uses genetic markers to indirectly determine the number of Rn or rn alleles a horse has.[1] The mutation responsible for true roan has not yet been identified exactly, but been assigned to equine chromosome 3 (ECA3) in the KIT sequence.[3] A roan zygosity test is reliable for American Quarter Horse, American Paint Horse, Welsh Pony, and Gypsy Cob.[1] Until a direct test is developed, the roan zygosity test may enable breeders to produce roans more reliably.
Homozygous roan
[edit]A 1979 study of American-bred Belgian draft horses found fewer roan offspring from roan-to-roan matings than expected for a simple dominant trait. Finding neither stillborn nor sickly, short-lived foals from these roan parents, the researchers concluded that in the homozygous condition the roan gene was lethal to the embryo or fetus.[27] Other studies at the time were using progeny ratios to identify potential lethality related to other coat colors, such as "dominant white" and "lethal white", so roan was believed to follow a similar pattern.[27] Genetic science in the 1970s could not provide a clear answer, as methods of molecular analysis had not yet been developed.[28]
The belief in "lethal roan" persisted until recently, when homozygous roan stallions with large numbers of offspring - all roan - were satisfactorily identified.[1] Homozygous roan stallions were identified in both European populations of Belgian horses in 1977, and in North American, in Quarter Horse stallions.[11][29]
In some breeds, homozygous roans can be identified by an indirect DNA marker test.[1] Such horses, with the genotype Rn/Rn, produce 100% roan offspring.[1] Homozygous roans and heterozygous roans (Rn/rn) are identical in appearance.[6]
Equine linkage group II
[edit]During the production of sex cells, DNA is "reshuffled" to ensure that the next generation does not inherit ancestral chromosomes as is, but a mixture of DNA from each parent. Paired chromosomes exchange parallel pieces of DNA, a process called chromosomal crossover, prior to being passed on to the next generation. When particular genes are located physically close together on a chromosome, they tend to be exchanged together. The rate at which two genes are passed on together can be used to calculate their distance from each other on the chromosome. Genes that tend to be passed on as a group form what is called a "linkage group".
Equine linkage group II includes a number of genes. The first linkage was found between a blood type marker and tobiano white spotting in 1978.[30] The same blood type marker, albumin, was linked to another blood protein called vitamin D-binding protein.[31] In 1982, a linkage grouping was proposed, including three genes for serum proteins, and three for coat color: tobiano spotting, chestnut, and roan.[32] Research since equine linkage group II was defined has identified the exact location of the tobiano allele and the chestnut allele.[33][34] The region of the chromosome that harbors the roan gene is homologous to parts of chromosomes in other species that also control coat color, even some similar to roan.[3] Presently, the KIT gene is the primary candidate gene for roan.[3] While a chromosomal inversion of KIT causes tobiano white spotting, KIT also harbors one or more alleles responsible for sabino spotting, no fewer than eleven alleles responsible for dominant white spotting, and is thought to be a major contributor to many other forms of less distinctive white markings.[16][35][36][37]
The effect of linkage between roan and chestnut is readily observed. If a horse possesses one chromosome with the wildtype nonchestnut allele and the dominant roan allele (E and Rn), while the other chromosome contains the recessive chestnut allele and the recessive nonroan allele (e and rn), it will outwardly appear blue roan, barring the influence of other genes. Normally, the chestnut and roan alleles would be separated during chromosomal crossover, but these two linked genes usually remain together. Such a horse will produce sex cells that are either E/Rn or e/rn. Mated to chestnut nonroan partners (e/rn), the horse would produce primarily blue roans, or chestnut nonroans, but few chestnut roans and few black nonroans.[4] If the recessive e and dominant Rn were on the same chromosome, though, the horse would be expected to produce primarily chestnut roans and nonchestnut nonroans with chestnut, nonroan partners.
Cultural/Historical References
[edit]The Blue Roan was a popular horse kept and ridden by the 10th Sikh Guru, Guru Gobind Singh during the late 17th-early 18th century. He was known as the "Blue Horse Rider" or "One Who Rides the Blue Horse" during his time.[citation needed]
See also
[edit]References
[edit]- ^ a b c d e f g h i j k l m "Roan Zygosity Test Information". Veterinary Genetics Laboratory Services. UC Davis. Retrieved 2009-10-01.
- ^ "Articles". New Jersey Pony Breeders and Owners. Archived from the original on 2009-10-14. Retrieved 2009-10-06.
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...blue roan comes on a dark (black, brown, or liver chestnut) background.
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The progressive loss of colour in the hair of grey horses is controlled by a dominantly inherited allele at the Grey locus (G^G). Foals are born any colour depending on the alleles present at other colour determining loci.
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Our association analysis indicated that the putative major gene for white markings is located at or near the KIT locus