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7 facts about frame overo genetics

It’s hard not to fall in love with a flashy Paint with frame overo markings—bright patches of horizontal white, each uniquely framed with contrasting color. But the beauty—and intrigue—of the pattern is more than skin deep.

The March 2015 Paint Horse Journal article “Perfectly Framed” took a deeper look at the Frame overo pattern to learn more about its causes and how it can be a colorful tool for Paint Horse breeders.

Curious about frame overo? Here’s seven things you need to know about this flashy pattern.

Photos by JD Waterhourse Photography
Seven Things You Need to Know About Frame Overo

  • The frame overo pattern is known for its placement of spots—often arranged horizontally—on the sides and the neck of the horse. The colored hair surrounding the white spots looks like a picture frame, lending the pattern its name.
  • Expression of the frame overo pattern can vary widely. Sometimes blue eyes (which pop up frequently in frame overos) are the only indication that a solid Paint-bred or otherwise solid-colored horse carries the gene. Frame overo is present in other breeds, including Quarter Horses.
  • Frame overos are heterozygous—carry one copy—for the Ile118Lys mutation of the endothelin receptor B (EDNRB) gene.
  • In the homozygous state, the same gene mutation is responsible for Lethal White Syndrome. However, only horses that are homozygous for the gene—meaning they received one copy of the allele from each parent—are affected by LWS. Carrying one copy of the mutation has no impact on the physical well-being of the horse.
  • Because the frame overo pattern can be combined with other patterns—or not expressed phenotypically at all—DNA testing is the only way to determine with certainty whether a horse is a frame overo.
  • The risk of LWS can be completely eliminated by testing all mares and stallions and not breeding carriers together. LWS is 100% preventable through education and responsible breeding.
  • The mechanism that controls the expression of the frame overo gene is still scientifically unknown, though some breeders believe a pedigree packed with color-producers is helpful.

Want to get your horse tested to see if he or she carries the Frame Overo mutation? All it takes is a simple DNA test and a few hair samples from his mane or tail. The Frame Overo test is included as part of APHA’s Comprehensive Disease Diagnostic test package (four tests for $100), the Comprehensive Coat Color test package (12 tests for $110) or individually for $25. To order a DNA Hair Kit from APHA’s MemberCare team, download the form at apha.com/forms/registration-forms or call (817) 222-6423.

The Paint Horse Journal is your leading source for Paint Horse-specific information. Subscribe or renew to the Paint Horse Journal so you never miss great articles like this one. Call (817) 222-6423 or visit phj.apha.com to learn more.


[Reprinting all or part of this news release is permitted, so long as credit is given to the Paint Horse Journal and a link provided back to apha.com.] 

About APHA

The American Paint Horse Association is the world’s second-largest international equine breed association, registering more than a million horses in 59 nations and territories since it was founded. APHA creates and maintains programs that increase the value of American Paint Horses and enriches members’ experiences with their horses.