Tobiano was the first type of white body spotting in horses recognized as being genetically distinct. Like other white markings, it varies widely in extent, with tobiano horses ranging from white with a colored head to normally colored with white hooves and lower legs, and perhaps a white area in the mane or tail. A few tobianos have blue eyes which are apparently produced by the tobiano gene.
The tobiano pattern has relatively crisp-edged white spots that cross the topline. The arrangement tends to be vertical, though not to the extent of a striped pattern. The head normally remains dark, though the white markings seen on non-spotted horses may be present. At times the dark skin extends under the edges of the white patches, giving a “halo” effect. Portions of the mane and tail growing from white areas are normally white, and in fact this may be the only obvious expression of tobiano in a minimally marked horse.
The pattern is due to a dominant allele, tobiano, at the tobiano locus, To. This locus is near but not at the KIT locus on chromosome 3, and a marker test is available. A horse with two copies of the tobiano allele is perfectly viable and not usually whiter than one with one tobiano and one wild-type allele. It is, however, more likely to show “paw prints” or “bear paws”–roan or spotted areas within the white patches.
Tobiano can occur on any base color: intense, dilute, or with interspersed white hairs. It does occasionally have an odd effect in the presence of one copy of the cream gene. The colored part of the coat “breaks up” into patches of dilute and non-dilute hair. This variation of the pattern is called calico. Calico is thought to be due to a dominant gene at a third locus which can only be detected if both tobiano and cream alleles are present. Theoretically, smoky calico should occur with areas of smoky, black, and white, but I cannot find any reference to this color in Sponenberg.
Although tobiano is dominant, tobiano foals are now and then produced by parents that appear non-spotted. On close examination one of these parents is generally a minimally marked tobiano, with extensive leg white and vary little face white.
The tobiano in the video is a good example of the pattern. Note the way the white markings on the neck are carried into the mane, and the way the white patches cross the topline.