WHAT IS TOBIANO?
The term 'tobiano' refers to the dominant gene that produces the tobiano spotting pattern in a majority of Spotted Saddle Horses. Since it is a dominant gene, at least one parent must be tobiano.
WHAT IS HOMOZYGOUS?
Homozygous is a term that means "two of the same." A horse can be homozygous for a wide variety of characteristics - the term is not limited to coat color. For example, when a person talks about his/her "homozygous stallion," and doesn't specify what the stallion is homozygous for, it could mean just about anything. That stallion could be homozygous for big ears, stifle problems, or the red factor gene. If a stallion owner says that his horse is "homozygous tobiano," then the term homozygous is describing the tobiano gene, meaning that the horse has two tobiano genes and will always produce tobiano (spotted) offspring.
In order for a horse to be homozygous for the tobiano gene, both sire and dam MUST be tobiano. It makes no difference how many spotted horses you can count on the pedigree; if one parent is solid, the horse CANNOT be homozygous tobiano. A blood test is available to determine if a horse is homozygous tobiano.