Genetic testing is a great tool for making smarter breeding decisions in the pursuit of color. By IRENE STAMATELAKYS
W
e all aim to breed the next running champion, but Paint breeders want both speed and color. What can you do to increase your chances of get-
ting a colored foal? You could just take a shot in the dark, or you could turn to genetic testing to reveal which color genes your stallion or mare carries. But with so many tests available, which ones do you need and which can you skip? Check out our guide to color pattern genetics, and improve your odds for color in your next speedster.
Tobiano
Want to bet on a sure thing? Then breed to a homozygous tobiano. Because the tobiano (TO) allele is dominant, the foal only needs to inherit one copy to be tobiano.
The tobiano gene is dominant, so a foal only needs to inherit one copy to display the pattern. A horse with one copy of the TO gene, like Hot Southern Mess, has a 50 percent chance of passing the tobiano pattern to her offspring. A horse with two copies of the TO gene is a homozygous tobiano and will always produce tobiano foals.
Genetic testing is the only way to know for sure if a horse is a homozy- gous tobiano.
If the horse is heterozygous for tobiano, there’s a 50 percent chance for tobiano offspring. If the horse is homozygous for tobiano, 100 percent of the offspring will be tobiano, virtu- ally eliminating the risk of a solid foal. For a horse to be a homozygous tobiano, both the sire and the dam must be tobianos or toveros and the horse in question must have inherited two copies of the TO gene. If either the
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sire or the dam does not carry the tobiano gene, then homozygosity is impossible. Some horses are minimal or
“slipped” tobianos and do not express enough white to meet APHA’s Regular Registry requirements. Others have lots of white—often because they carry multiple white patterns—making it difficult to tell visually whether they are tobiano carriers. In either case, if they do carry the tobiano gene, they have the same potential to transmit the TO allele to foals.
Frame Overo/OLWS
The frame overo pattern, quite com- mon in the Paint Horse breed, is caused by a mutation of the EDNRB gene. Foals receiving one copy of the mutated
APHA FILE PHOTO
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