What does it mean to be homozygous tobiano?
The tobiano modifier gene is a dominant gene and it only takes 1 copy for the foal to be a colored tobiano pinto. When a homozygous tobiano (TOTO) is bred with a solid (toto) the result is always a colored tobiano foal with the geneotype of ( TOto). 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 chromosome 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’ 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 whereby a horse has
