What is Homozygous?

From Comptom's Interactive Encyclopedia:

Homozygous: A plant or animal having two identical alleles at a single locus on a chromosone, and hence breeding true type for the particular character involved; purebred

Homozygous?


What does this mean in "horse" terms? It means that it is genetically impossible for a horse that tests homozgous for the Tobiano gene to produce a solid or overo foal, regardless of the mare he/she is bred to. Having at least one homozygous parent guarantees that a foal will have a Tobiano or Tovero coat pattern. Having two homozygous parents guarantees that a foal will itself be homozygous for the Tobiano gene.

A horse can also be homozygous for the Black gene. What this means is that it is impossible for a horse that tests homozygous for the Black gene to produce a red foal (sorrel, chestnut, red roan, red dun). Breeding to a horse that is homozygous for the Black gene means that in most cases the resulting foal will be Black. Foals can also be Bay, Grulla, Buckskin, Dun, Blue Roan, or Gray.