Genetics
Tobiano is a dominant 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 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, 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.
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