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
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.