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Breeds: All
Description
Tobiano is one of the most common white spotting patterns in horses. Tobiano horses typically have large, rounded white patches with smooth, clean edges, white legs, and white that crosses the back between the withers and the tail. The head is usually colored like a solid horse, although white from other genes, such as a blaze, can also appear on the face.
Tobiano is caused by a large chromosomal inversion, where a section of chromosome 3 near the KIT gene is flipped end to end. The inversion is believed to disrupt the regulation of KIT, a gene needed for pigment cells to develop, which produces the white areas. KIT is also involved in several other white patterns, including sabino, roan and dominant white. The tobiano inversion was identified by researchers at the University of Kentucky and has been found only in tobiano horses.
One copy or two
Tobiano is dominant, so a single copy produces the pattern. Horses with one copy (n/T) pass tobiano to about half of their foals on average. Horses with two copies (T/T) always pass one copy on, so every foal will be tobiano regardless of its other parent.
T/T horses sometimes show small, rounded dark spots within their white areas or colored patches, often called “ink spots” or “paw prints.” These can be a clue, but they are not reliable, so genetic testing is the only way to know for certain whether a tobiano horse carries one copy or two.
Why test for tobiano?
Testing confirms tobiano in horses whose pattern is minimal or hidden by other white patterns, and identifies T/T horses, which are valuable for breeding because they guarantee tobiano foals. Animal Genetics’ test is based on the tobiano inversion together with additional KIT markers identified by our own researchers.
Possible results
| Genotype | Description |
|---|---|
| T/T | Homozygous: Horse has two copies of tobiano and shows the tobiano pattern. Horse will pass one copy to every offspring, so all foals will be tobiano. |
| n/T | Heterozygous: Horse has one copy of tobiano and shows the tobiano pattern. Each foal has a 50% chance of inheriting it. |
| n/n | Negative: Horse does not carry tobiano. |
Breeds Affected
American Paint Horse, Pinto, Miniature Horse, Shetland Pony, Gypsy Vanner, Tennessee Walking Horse, Missouri Fox Trotter, Icelandic Horse, Mustang, Spotted Saddle Horse, Spotted Draft Horse, Welsh Pony, Warmblood
Reference
A chromosome inversion near the KIT gene and the Tobiano spotting pattern in horses.
Cytogenet Genome Res. 2007;119(3-4):225-30. doi: 10.1159/000112065. Epub 2008 Feb 1.
PMID: 18253033
Related Tests
Breeding for white patterns? The Pattern Panel includes tobiano plus seven other pattern tests for $75.