Tobiano foals with only one spotted parent will not breed true for tobiano because they have received a not-tobiano gene from their solid parent that they will pass on, at random, to half of their progeny. Breeders that can recognize homozygotes may use them to design subsequent matings so that every foal has the tobiano pattern. No direct genetic test for the tobiano gene, such as a DNA test, is available. A test of markers linked to the tobiano gene is available that often can identify horses likely to be homozygous for tobiano. To access the instructions and tobiano test forms necessary to submit samples.
All animals carry two copies of each gene.
One is inherited from the dam and one from the sire. Markers that are expressed by a single letter indicate the marker inherited from the dam and the sire are identical or homozygous. Al and Gc are genes that are linked to the tobiano-spotting pattern. There is no direct test for tobiano, but if the linked markers are informative then it is possible to predict zygosity for the tobiano gene. The term informative applies to a horse heterozygous for tobiano whose Al and Gc markers are heterozygous or not the same.