Description

Courtesy of Linda Brown - Wizards Spell Ranch

The Tobiano (pronounced: tow be yah' no) coat pattern usually involves some white on all four legs and rounded white spots on the body with sharp, clean edges. The head of the horse is usually colored and will not have white caused by the Tobiano gene. The white on the body will generally cross the topline of the horse.
The Tobiano coat pattern is governed by a dominant gene, meaning that there only needs to be one copy of the gene (tobiano heterozygous-nT) for the tobiano coat pattern to be present. Homozygosity of the tobiano gene (TT-two copies of the tobiano gene) may show visual clues ("ink spots" or "paw prints") but only genetic testing will tell you more conclusively that the horse is homozygous for the Tobiano gene. When there is no presence of the tobiano gene (homozygous negative-nn), the tobiano coat pattern is not possible.

TT - Tobiano Homozygous - Tobiano coat pattern present

nT - Tobiano Heterozygous - Tobiano coat pattern present

nn - Homozygous Negative - no Tobiano coat pattern present

This chart shows the possibilities of offspring when mating two horses.

Tobiano Testing

We now test for several genetic markers that have been found to be strongly linked to the tobiano coat pattern. In 2002, researchers at the University of Kentucky, led by Dr. Samantha Brooks, located a SNP within the KIT gene that is closely linked to the Tobiano pattern. Since then, additional markers have been found within the KIT gene by researchers here at Animal Genetics that we also use to determine Tobiano zygosity. Most recently, researchers at the University of Kentucky discovered a large chromosomal inversion on chromosome 3 near the KIT gene of Tobiano horses. This inversion, which has only been found in Tobiano horses, is believed to disrupt the normal functioning of the KIT gene and cause the Tobiano pattern.

 
References:

Brooks SA, Lear TL, Adelson DL, Bailey E. A chromosome inversion near the KIT gene and the Tobiano spotting pattern in horses. Cytogenet Genome Res. 2007;119(3-4):225-30. Epub 2008 Feb 1.

Brooks, SA, RB Terry, and E. Bailey A PCR-RFLP for KIT associated with tobiano spotting pattern in horses. Animal Genetics 2002:33(4):301-3.

Cost

$25.00 US per sample.

Collect sample by pulling (not cutting) 20-30 mane or tail hairs with roots attached. It is important that you pull the hairs and confirm that the actual root of the hair is being collected. The root contains the genetic material of your horse that is needed for DNA testing. Therefore, cut hairs do not provide an adequate sample of your horse. Place the collected hairs of each horse in a separate zip-lock bag labeling the bags accordingly with the horses name or identification number. Download and complete a submission form for each sample and send along with payment to Animal Genetics for testing.

Results

Results are given using the following symbolic notation: