# Overo > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Overo > Markdown URL: https://mediated.wiki/source/Overo.md > Source: https://en.wikipedia.org/wiki/Overo > Source revision: 1303493210 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) {{Short description|Group of colouration patterns of horses}} thumb|A frame overo '''Overo''' refers to several genetically unrelated [pinto](/source/pinto_horse) coloration patterns of white-over-dark body markings in [horse](/source/horse)s, and is a term used by the [American Paint Horse Association](/source/American_Paint_Horse_Association) to classify a set of pinto patterns that are not [tobiano](/source/tobiano). ''Overo'' is a Spanish word, originally meaning "like an egg".[http://www.apha.com/forms/PDFFiles/guidebooks/07ColorGen.pdf ''American Paint Horse Association's Guide to Coat Color Genetics'' American Paint Horse Association, 2007.] {{webarchive|url=https://web.archive.org/web/20081011220117/http://www.apha.com/forms/PDFFiles/guidebooks/07ColorGen.pdf |date=2008-10-11 }} Accessed August 19, 2008 The most common usage refers to '''frame overo''', but '''[splashed white](/source/splashed_white)''' and '''[sabino](/source/sabino_horse)''' are also considered "overo".[http://www.apha.com/breed/geneticeq3.html "Genetic Equation: The overo patterns" ''American Paint Horse Association''.] {{webarchive|url=https://web.archive.org/web/20080907031343/http://www.apha.com/breed/geneticeq3.html |date=2008-09-07 }} Web page accessed August 19, 2008[http://www.vgl.ucdavis.edu/services/coatcolorhorse.php "Horse coat color tests"] {{Webarchive|url=https://web.archive.org/web/20090615220714/http://www.vgl.ucdavis.edu/services/coatcolorhorse.php |date=2009-06-15 }} from the [University of California, Davis](/source/University_of_California%2C_Davis) Veterinary Genetics Lab A horse with both tobiano and overo patterns is called [tovero](/source/tovero). Frame overo, splashed white, and sabino are three separate pinto patterns, genetically unrelated, that are grouped together under the name "overo". The frame overo pattern tends to have white spots on the flanks and face, surrounded by a dark "frame" of color. If two horses with the frame overo gene are bred together, there is a 25% chance the foal will have [lethal white syndrome](/source/lethal_white_syndrome).{{cite web|url=https://vgl.ucdavis.edu/test/lethal-white-overo | title=Lethal White Overo (LWO) | access-date=December 20, 2021}} Splashed white or splash overo is a group of patterns that tend to have white on the underside, as if a horse ran through white paint with its head lowered. So far 6 alleles on two genes have been discovered to cause splashed white patterns. There is a correlation between the splashed white pattern and deafness.{{cite web|url=https://vgl.ucdavis.edu/test/splashed-white |title= Splashed White Mutations – SW1, SW2, SW3, SW4, SW5, and SW6 |access-date=December 20, 2021}} Sabino or sabino overo is a group of patterns that typically have white on the legs, face, and sometimes also belly, often with white ticking or roaning. Several alleles on the [KIT gene](/source/dominant_white) are known to cause sabino or sabino-like patterns.{{cite web|url=https://vgl.ucdavis.edu/test/sabino-1|title= Sabino 1 | access-date=December 20, 2021}}{{cite web |url=https://www.etalondx.com/dominant-white |access-date=December 20, 2021 |title=More about Dominant White}} ==Frame overo== {{Main|Lethal white syndrome}} thumb|Frame overos have sharply defined, irregular, horizontally oriented white patches. As here, they are often bald-faced and white patches seldom cross the topline, creating a "frame" of non-white coat. The '''frame overo''' pattern is the most common of the three types of overo patterns recognized in the [American Paint Horse](/source/American_Paint_Horse) breed. A frame overo horse appears to be any solid base color (bay, black, chestnut, etc.) with white irregular patches added, usually with a horizontal orientation. [Markings](/source/Horse_markings) are often of jagged shape rather than rounded, the white rarely crosses the back, the lower legs tend to be dark, and the tail is one color, usually dark. The head is often white or bald-faced, and blue eyes are not uncommon. The frame overo pattern usually behaves like a [dominant](/source/dominance_relationship) gene, in that when frame overo horses are crossed on nonspotted horses, about half of the foals come out spotted. There are records of frame overos being produced by two nonspotted parents. There is a theory, however, that these "solid" horses simply may be horses with very minimal expression of overo genetics. Frame coloring is controversial because it is associated with [lethal white syndrome](/source/lethal_white_syndrome) (OLWS or LWS),[http://www.aegrc.uq.edu.au/index.html?page=30053 " Overo-Lethal White Foal Syndrome (OLW)"] {{webarchive|url=https://web.archive.org/web/20080721000432/http://www.aegrc.uq.edu.au//index.html?page=30053 |date=2008-07-21 }}, University of Queensland, web page accessed December 1, 2007 the equine version of [Hirschprung disease](/source/Hirschprung_disease). LWS occurs when a [foal](/source/foal) is [homozygous](/source/homozygous) for the Ile118Lys EDNRB mutation, which is considered by many researchers to be "usually responsible" for the frame overo [phenotype](/source/phenotype).{{cite journal |vauthors=Santschi EM, Vrotsos PD, Purdy AK, Mickelson JR |title=Incidence of the endothelin receptor B mutation that causes lethal white foal syndrome in white-patterned horses |journal=Am J Vet Res |volume=62 |issue=1 |pages=97–103 |date=Jan 2001 |pmid=11197568 |doi=10.2460/ajvr.2001.62.97 |doi-access=free }} However, other researchers emphasize that overo spotting patterns are phenotypically and genetically [heterogeneous](/source/heterogeneous), that is, may have multiple sources.[http://www.vgl.ucdavis.edu/services/coatcolorhorse.php "Horse Coat Color Tests" ''Veterinary Genetics Laboratory,'' University of California, Davis.] {{Webarchive|url=https://web.archive.org/web/20090615220714/http://www.vgl.ucdavis.edu/services/coatcolorhorse.php |date=2009-06-15 }} web page accessed August 21, 2008 The frame overo gene can be masked by other white patterns, particularly [tobiano](/source/tobiano), which is a dominant gene and [epistatic](/source/Epistasis) to overo.{{cite journal |vauthors=Metallinos DL, Bowling AT, Rine J |title=A missense mutation in the endothelin-B receptor gene is associated with Lethal White Foal Syndrome: an equine version of Hirschsprung disease |journal=Mamm. Genome |volume=9 |issue=6 |pages=426–31 |date=Jun 1998 |pmid=9585428 |url=http://link.springer-ny.com/link/service/journals/00335/bibs/9n6p426.html |doi=10.1007/s003359900790 |url-status=dead |archiveurl=https://web.archive.org/web/20000916124713/http://link.springer-ny.com/link/service/journals/00335/bibs/9n6p426.html |archivedate=2000-09-16 |url-access=subscription }} '''Epistatic''' means that when both genes are present, this is the one expressed. In addition, some carriers of the LWS allele appear to be solid. One theory holds that such horses carry the frame gene, but so minimal in expression that they appear solid. Either way, all LWS foals have horses with frame overo patterning in their pedigrees, and horses carrying a frame allele may not necessarily have a visible expression of the frame overo color. ==="Lethal white"=== {{Main|Lethal white syndrome}} Foals which are [homozygous](/source/homozygous) for frame and thus have [lethal white syndrome](/source/lethal_white_syndrome) (LWS) are not [albino](/source/albino)s. Albinism does not exist in horses.{{cite journal |last=Castle |first=William E. |title=The Abc of Color Inheritance in Horses |journal=Genetics |volume=33 |issue=1 |pages=22–35 |url=http://www.genetics.org/cgi/reprint/33/1/22 |quote=No true albino mutation of the color gene is known among horses, though several varieties of white horse are popularly known as albinos. |year=1948 |doi=10.1093/genetics/33.1.22 |pmid=17247268 |pmc=1209395 |access-date=2010-08-10 |archive-url=https://web.archive.org/web/20100902192728/http://www.genetics.org/cgi/reprint/33/1/22 |archive-date=2010-09-02 |url-status=live }} LWS foals are born almost or completely white with pink skin, but have blue eyes, not red ones. The lethal trait is that the nerves of the foal's [digestive system](/source/digestive_system) are undeveloped and the bowel cannot move food along. All lethal white foals die within 72 hours after birth, and are typically [euthanized](/source/Animal_euthanasia) sooner for humane reasons. A horse can be a carrier of the trait when it carries only one copy of the gene, (that is, [heterozygous](/source/heterozygous)) and carriers are healthy and show no clinical signs of lethal white syndrome. Thus, it is recommended by organizations such as the [American Paint Horse Association](/source/American_Paint_Horse_Association) that horses of any pattern with overo ancestors be tested to verify their carrier state before being bred. There is a [DNA](/source/DNA) test for the gene which can be used to plan breedings and avoid producing affected foals. The mutation has not been found in solid-colored horses from breeds without frame patterning. Likewise, a sick foal that happens to be white can be tested to avoid inadvertent euthanization of a non-lethal foal who has a simple case of [colic](/source/horse_colic). Lethal white horses should not be confused with non-lethal forms of [white](/source/white_(horse)), such as [dominant white](/source/dominant_white), which may be completely white with pink skin. Blue-eyed, pink-skinned [cremello](/source/cremello)s and other horses carrying the [cream gene](/source/cream_gene) do not carry the LWS allele unless they also have an ancestor with overo genetics. The [splash white](/source/Splashed_white) and [sabino](/source/sabino_horse) genetics are not associated with lethal white, though such horses could also be carriers of the frame allele. ==Splash overo== {{Main|Splashed white}} thumb|right|A splash overo with some minor sabino traits A ''splash'' or ''splashed white'' overo pattern appears like a solid-colored horse who has been dipped in white paint, and the color splashed up from the bottom. It is the least common of the overo patterns. The legs and bottom portion of the body are usually white, as is the head, and blue eyes are common. Edges where white and dark color meet are usually crisp and sharp. Recent studies suggest that splashed white may be caused by a dominant gene. Splash overos are more prone to being deaf than other horses.[http://www.apha.com/breed/geneticeq5.html APHA Genetic Equation: Splashed White] {{webarchive|url=https://web.archive.org/web/20090402205421/http://www.apha.com/breed/geneticeq5.html |date=2009-04-02 }} Outside of the United States, the term "splash" is sometimes applied to horses of apparent Sabino patterning. ==Sabino "overo"== thumb|upright|A Sabino, called "sabino overo" by some registries {{main|Sabino horse}} ''[Sabino](/source/Sabino_horse)'' is listed a type of overo coloring by the [American Paint Horse Association](/source/American_Paint_Horse_Association).[http://www.apha.com/breed/geneticeq4.html APHA Genetic Equation, "Sabino Spotting"] {{webarchive|url=https://web.archive.org/web/20120616160852/http://www.apha.com/breed/geneticeq4.html |date=2012-06-16 }} This terminology, outdated in terms of modern genetics, creates confusion, because other breeds, including many that will not register "pinto" or "paint" horses, may have individuals with sabino genetics. One reason for the terminology confusion is that "overo" was used by Paint horse breeders in the United States to refer to "anything that is not tobiano." Another reason for this terminology is that the term "overo", when used outside of the US, particularly in [Spanish](/source/Spanish_language)-speaking countries, refers to horses with the speckled [roan](/source/roan_(color))ing patterns typical of horses called [sabino](/source/sabino_horse) in the USA. In addition, strongly marked sabino horses may mimic either overo or tobiano coloring. In general, sabino is a generic description for a group of similar white spotting patterns. These include high white stockings on all four feet, often extending up the legs with jagged edges, a fairly white head, with [markings](/source/horse_markings) often extending past the eyes, roaning at the edges of white markings, lip spots, "lacing," and white patches on the lower barrel that may extend to the flanks. A minimal sabino may only have one of the traits associated with [sabino](/source/sabino_horse) horses. On the other hand, a "sabino-white" is a near-white or completely white horse, and sabino genetics are not linked to [lethal white](/source/lethal_white_syndrome). ==Tobiano== thumb|The tobiano pattern {{Main|Tobiano}} [Tobiano](/source/Tobiano) coloring is the inverse of overo spotting. Tobianos have a vertical spotting pattern, large, rounded spots, white that crosses the topline, dark heads, but mostly white legs and white or multi-colored tail. Typical examples tend to have more white than dark, whereas typical frame overo horses tend to more dark than white, though there are many exceptions in both cases. It is created by a different gene from any of the overo patterns and is a [dominant gene](/source/dominant_gene). All tobianos must have at least one tobiano parent. When a tobiano [allele](/source/allele) is present, it is [epistatic](/source/Epistasis) and often masks other patterns. ==Tovero and other mixed patterns== {{Main|Tovero}} A [tovero](/source/tovero) horse has pinto spotting patterns that show characteristics of both overo and [tobiano](/source/tobiano) and probably carries genes for both. For example, a tovero might have tobiano body spotting with rounded edges and white across the back, yet have irregular facial markings and blue eyes. Horses may also have a combination of sabino and frame overo genetics or any other combination of genes, resulting patterns that are difficult to smoothly classify into any one group. ==Gallery== File:Miniature Horse Runs Through the Pasture.jpg|Miniature frame overo File:Overo.jpg|Frame overo foal ==See also== *[Pinto horse](/source/Pinto_horse) *[American Paint Horse](/source/American_Paint_Horse) *[Lethal white syndrome](/source/Lethal_white_syndrome) *[Equine coat color](/source/Equine_coat_color) *[Equine coat color genetics](/source/Equine_coat_color_genetics) ==References== {{reflist}} *{{cite journal |author1=Paul D. Vrotsos RVT |author2=Elizabeth M. Santschi DVM |title=Stalking the Lethal White Syndrome |journal=Paint Horse Journal |date=Jul 1998 |url=http://www.apha.com/breed/lethalwhites03.html |url-status=dead |archiveurl=https://web.archive.org/web/20081026125923/http://www.apha.com/breed/lethalwhites03.html |archivedate=2008-10-26 }} *[http://www.vgl.ucdavis.edu/services/coatcolorhorse.php "Horse coat color tests"] from the [University of California, Davis](/source/University_of_California%2C_Davis) Veterinary Genetics Lab *[http://www.vgl.ucdavis.edu/services/coatcolor.php "Introduction to Coat Color Genetics"] ''from'' Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis. Web Site accessed January 12, 2008 ==External links== {{commonscat}} *[https://web.archive.org/web/20051212154223/http://www.geocities.com/Baja/Outback/2936/SplashedW.html "Splashed White horses, Min to Max expression"] Web Site Accessed August 18, 2008 * [http://www.apha.com American Paint Horse Association] * [http://www.pinto.org Pinto Horse Association of America] * [http://www.sshbea.org Spotted Saddle Horse Breeders & Exhibitors Association] {{Equine coat colors}} {{Authority control}} Category:Horse coat colors --- Adapted from the Wikipedia article [Overo](https://en.wikipedia.org/wiki/Overo) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Overo?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.