RARE COLOR RULES

Discover some of the rarest horse colors and the genetics behind them.

- BY MICAELA MYERS

When Rebecca Bellone was in college in the 1990s, she took a class on livestock genetics. The professor showed a picture of a spotted Appaloosa, and revealed to the class that they didn't currently understand how Appaloosas passed down their white patterning from parents to foal.

Rebecca thought the Appaloosa was the most beautiful horse she'd seen, and soon bought one of her own. She also decided to become a scientist to study equine genetics, particularly pigmentation.

She now holds a Ph.D. from the University of Kentucky and directs the Veterinary Genetics Laboratory at University of California, Davis. The lab tests horses and other species to verify their parentage, rare coat color genes, and more.

COLOR GENE BASICS

All horses are either black-based or red-based, determined by an extension gene ("E") and the agouti gene ("A"). The dominant version of the extension gene ("E") is responsible for creating a black base, while the recessive version ("e") is responsible for creating a red base. (See "Gene Basics" sidebar if you're not familiar with dominant and recessive genes.)

"The dominant version of the agouti gene ('A') limits black pigment on a black-based horse to the points, whereas the recessive version of agouti ('a') results in an all-black phenotype on horses with two copies," Rebecca says.