Tobiano is a spotted color pattern commonly seen in

pinto horse A pinto horse has a coat color that consists of large patches of white and any other color. The distinction between "pinto" and "solid" can be tenuous, as so-called "solid" horses frequently have areas of white hair. Various cultures through ...

s, produced by a

dominant gene In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and t ...

. The tobiano

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...

produces white-haired, pink-skinned patches on a base coat color. The coloration is almost always present from birth and does not change throughout the horse's lifetime, unless the horse also carries the

gray Grey (more common in British English) or gray (more common in American English) is an intermediate color between black and white. It is a neutral or achromatic color, meaning literally that it is "without color", because it can be composed o ...

gene. It is a

, so any tobiano horse must have at least one parent who carries the tobiano gene. Other spotting patterns seen in pinto horses include frame overo, splashed white and sabino. In the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...

, tobianos are frequently referred to as "coloured" or as "pied":

piebald A piebald or pied animal is one that has a pattern of unpigmented spots (white) on a pigmented background of hair, feathers or scales. Thus a piebald black and white dog is a black dog with white spots. The animal's skin under the white backgro ...

if black and white,

skewbald Skewbald is a colour pattern of horses. A skewbald horse has a coat made up of white patches on a non-black base coat, such as chestnut, bay, or any colour besides black coat. Skewbald horses which are bay and white (bay is a reddish-brown colou ...

if white and any base color other than black. Sometimes "painted" is also used. Bay and white tobiano horses are also referred to as tricoloured.

Characteristics

Tobiano traits generally include the following: * White legs from the hocks and knees down * White crossing the back between the withers and the dock of the tail * White is arranged in a vertical pattern * Facial markings are similar to those of a traditionally solid-colored horse. i.e. star, snip, strip, or blaze. Extreme white facial markings suggest the presence of additional color pattern genes beyond tobiano * White patches which are usually rounded or oval in shape, rather than jagged (see

overo Overo refers to several genetically unrelated pinto coloration patterns of white-over-dark body markings in horses, and is a term used by the American Paint Horse Association to classify a set of pinto patterns that are not tobiano. ''Overo'' is ...

) * Dark color extending down the neck, giving the appearance of a shield The word ''tobiano'' is of

Portuguese Portuguese may refer to: * anything of, from, or related to the country and nation of Portugal ** Portuguese cuisine, traditional foods ** Portuguese language, a Romance language *** Portuguese dialects, variants of the Portuguese language ** Portu ...

origin, first used in Brazil to describe horses brought to Farroupilha's War by Brigadeiro Rafael Tobias de Aguiar. (HOUAISS, A. VILLAR, M. de S. Dicionário Houaiss da Língua Portuguesa. Rio de Janeiro: Objetiva, 2001. p. 2727).

Genetics

Tobiano is a dominant gene, designated ''TO''. Therefore, one parent must be a tobiano for the pattern to occur, and the coat pattern will occur with a single copy of the tobiano gene present (i.e. the horse is

heterozygous Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. Mo ...

for tobiano). Furthermore, when a horse is

homozygous Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. Mo ...

for tobiano coloring, all of that horse's offspring will be spotted, with only a few exceptions: if either parent passes the dominant

gene to the foal, then its spots will be visible while it is young, but will gradually become lighter until finally, as the gray gene acts upon all coat colors, the entire horse's coat fades. In the case of horses that are born tobiano but turn gray, the skin will retain pigmented and unpigmented skin beneath its hair that may produce "ghost" markings. A homozygous tobiano that also carries a dilution gene, such as a pinto with a base color of palomino or buckskin, may not reliably produce spotted offspring if bred to another horse with a dilution gene, as a double-dilution may "wash out" the base color. The tobiano gene itself is not linked to

lethal white syndrome Lethal white syndrome (LWS), also called overo lethal white syndrome (OLWS), lethal white overo (LWO), and overo lethal white foal syndrome (OLWFS), is an autosomal genetic disorder most prevalent in the American Paint Horse. Affected foals are bo ...

. However, some tobiano horses may be carriers of the gene if they have

ancestors, and thus have produced affected offspring when bred to another horse that is also a carrier. In some cases, a horse which carries both tobiano and overo genetics may display white markings that combine both patterns, and are referred to as

tovero The Tovero (also known as Tobero)PHAA
Retrieved on 13 January 2009 c ...

DNA testing

Tobiano occurs due to a chromosomal inversion on ECA3 where the gene order of a section spanning nearly one-third of the chromosome "flipped" during a

genetic recombination Genetic recombination (also known as genetic reshuffling) is the exchange of genetic material between different organisms which leads to production of offspring with combinations of traits that differ from those found in either parent. In eukaryo ...

event. It is thought to be an ancient gene among domestic horses, about 3500 years old, and is widely distributed across many breeds in the world.

Genetic testing Genetic testing, also known as DNA testing, is used to identify changes in DNA sequence or chromosome structure. Genetic testing can also include measuring the results of genetic changes, such as RNA analysis as an output of gene expression, or ...

is available to help determine the presence of the tobiano gene. Originally, there was no direct test for tobiano; the early tobiano tests utilized six

genetic markers A genetic marker is a gene or DNA sequence with a known location on a chromosome that can be used to identify individuals or species. It can be described as a variation (which may arise due to mutation or alteration in the genomic loci) that can ...

, including a marker on the ''KIT'' gene on horse

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

3, which were closely linked to tobiano but could not be used to officially prove

homozygosity Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. ...

. After some years of research from the University of Kentucky, in 2008 the chromosomal inversion that affects regulatory regions of the ''KIT'' gene was discovered."DNA Testing for Tobiano"
''from'' Animal Genetics Incorporated This inversion was finally mapped for genetic testing and is now offered by several laboratories. Testing is most often intended to determine homozygosity, but is also useful in cases where a horse has grayed, or if a horse has an unexplained loss of pigmentation.

Characteristics

Genetics

DNA testing

See also

References

Further reading