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. However, some tobiano horses may be carriers of the gene if they have overo 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 toveros. 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 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 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. 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. 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. See also American Paint Horse Equine coat color genetics Equine coat color Overo Pinto horse Sabino horse References Further reading "Horse coat color tests" from Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis. Web Site accessed January 12, 2008 "Introduction to Coat Color Genetics" from Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California, Davis. Web Site accessed January 12, 2008 Horse coat colors