Tobiano
Encyclopedia
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 throughout history appear to have selectively bred for pinto...
s, produced by a dominant gene. The tobiano gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
produces white-haired, pink-skinned patches on a base coat color. The coloration is present from birth and does not change throughout the horse's lifetime, unless the horse also carries the gray
Gray (horse)
Gray or grey is a coat color of horses characterized by progressive silvering of the colored hairs of the coat. Most gray horses have black skin and dark eyes; unlike many depigmentation genes, gray does not affect skin or eye color Their adult hair coat is white, dappled, or white intermingled...
gene. (see below)
Other spotting patterns seen in Pinto horses include overo
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...
and the sabino
Sabino horse
Sabino is a group of white spotting patterns in horses that affect the skin and hair. A wide variety of irregular color patterns are accepted as sabino. In the strictest sense, "sabino" refers to the white patterns produced by the Sabino 1 gene, for which there is a DNA test...
markings. In the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
, Tobianos are frequently referred to as "Coloured" or as Piebald
Piebald
A piebald or pied animal is one that has a spotting pattern of large unpigmented, usually white, areas of hair, feathers, or scales and normally pigmented patches, generally black. The colour of the animal's skin underneath its coat is also pigmented under the dark patches and unpigmented under...
(black and white) or Skewbald
Skewbald
Skewbald is a color 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 color besides black coat. Skewbald horses which are bay and white are sometimes called tricoloured...
(white and any base color other than black). However, Bay and white horses are also referred to as Tri-Coloured.
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 OveroOveroOvero 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...
) - Dark color extending down the neck, giving the appearance of a shield
Genetics
Tobiano is a dominantDominance relationship
Dominance in genetics is a relationship between two variant forms of a single gene, in which one allele masks the effect of the other in influencing some trait. In the simplest case, if a gene exists in two allelic forms , three combinations of alleles are possible: AA, AB, and BB...
gene. 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 for Tobiano). Furthermore, when a horse is homozygous for Tobiano coloring, all of that horse's offspring will be spotted, with only a few exceptions: If either parent passes the dominant gray
Gray (horse)
Gray or grey is a coat color of horses characterized by progressive silvering of the colored hairs of the coat. Most gray horses have black skin and dark eyes; unlike many depigmentation genes, gray does not affect skin or eye color Their adult hair coat is white, dappled, or white intermingled...
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 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
Dilution gene
Dilution gene is a popular term for any one of a number of genes that act to create a lighter coat color in living creatures. There are many examples of such genes:-General:...
, such as a Pinto with a base color of palomino
Palomino
Palomino is a coat color in horses, consisting of a gold coat and white mane and tail. Genetically, the palomino color is created by a single allele of a dilution gene called the cream gene working on a "red" base coat...
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
Lethal white syndrome , also called overo lethal white syndrome , lethal white overo , and overo lethal white foal syndrome , is an autosomal genetic disorder most prevalent in the American Paint Horse...
. However, some Tobiano horses may be carriers of the gene if they have overo
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...
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
Tovero
The Tovero coloration is a mix of tobiano and overo colorations in Pinto horses and American Paint Horses. The genetics of pinto coloration are not always fully understood, and some horses have a combination of patterns that does not fit cleanly in either category.Some characteristics of a Tovero...
s.
DNA Testing
Genetic testing 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, including a marker on the KIT gene on Horse chromosomeChromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
3, which were closely linked to Tobiano but could not be used to officially prove homozygosity. However, in 2008 it was determined after some years of research from the University of Kentucky, that Tobiano coat pattern is the result of a chromosomal 'inversion' that affects regulatory regions of the KIT gene. This inversion was finally mapped for genetic testing and is now offered by some laboratories as a more direct Tobiano assay. Testing is most often intended to determine Homozygosity, but is also useful in cases where a horse has greyed out, or if a horse has an unexplained loss of pigmentation.
See also
- Equine coat color geneticsEquine coat color geneticsEquine coat color genetics determine a horse's coat color. There are many different coat colors possible, but all colors are produced by the action of only a few different genes. The simplest genetic default color of all domesticated horses can be described as either "red" or "non-red", depending...
- Equine coat colorEquine coat colorHorses exhibit a diverse array of coat colors and distinctive markings. A specialized vocabulary has evolved to describe them.While most horses remain the same color throughout life, a few, over the course of several years, will develop a different coat color from that with which they were born...
- Pinto horsePinto horseA 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 throughout history appear to have selectively bred for pinto...
- OveroOveroOvero 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...
- Sabino horseSabino horseSabino is a group of white spotting patterns in horses that affect the skin and hair. A wide variety of irregular color patterns are accepted as sabino. In the strictest sense, "sabino" refers to the white patterns produced by the Sabino 1 gene, for which there is a DNA test...
- American Paint HorseAmerican Paint HorseThe American Paint Horse is a breed of horse that combines both the conformational characteristics of a western stock horse with a pinto spotting pattern of white and dark coat colors. Developed from a base of spotted horses with Quarter Horse and Thoroughbred bloodlines, the American Paint Horse...