WHAT IS HOMOZYGOUS?
A tobiano horse that is homozygous will ALWAYS
throw a spotted coat pattern or a tobiano coat pattern in their offspring. Even if the
other parent has a solid, overo, or tobiano coat pattern, the homozygous tobiano gene will
be dominant in the offspring's coat color. The tobiano gene is an inherited dominant gene.
To determine if a horse is homozygous, you must evaluate the following:
1. Pedigree: Both parents must be tobiano.
2. Phenotype: The horse should have secondary body spotting such as "ink spots" or "paw print".
3. Test Breeding: The horse should have no solid offspring from solid mates.
4. Studbook Data: The horse has no solid offspring.
5. Genetic Marker Analysis: Genetic testing by approved laboratory.
The EE Paint Horse
What Is Black Pigment Gene?
A red coat color in horses is well-documented
to be inherited as a trait recessive to black. A diagnotic test for the red factor, based
on DNA analysis, provides the information to determine what color offspring a horse can
throw. The absence of the red factor presents itself as "E".
"E" - No red factor was detected. The horse can be assumed to be homozygous for black pigment (EE). It cannot have red foals (sorrel or chestnut) regardless of the color of the mate. The basic color of the horse will be black, bay or brown, but may also have buckskin, zebra dun, grulla, perlino, gray, white or any of these colors with the white hair patterns of tobiano (for Paints).
For more indepth information on Homozygous & Black Pigment see Veterinary Genetics - UC Davis.