Frame overo
Frame overo (oh-VAIR-oh) is a pinto pattern. It adds white patches to the face, flanks, and sides of the neck, but leaves a darker "frame" of color around the white. Like other pinto patterns, the non-white areas can be any base color depending on what other genes the horse has.
The frame overo gene also causes Lethal White Syndrome (LWS). A horse with one copy of the frame overo gene will have the frame pinto pattern, but a horse with two copies will have lethal white syndrome. Lethal white foals are fully white with pink skin, and die at a young age due to an underdeveloped colon.
| Chestnut background (e/e) | Bay background (E/_ A/_) | Black background (E/_ a/a) | |
|---|---|---|---|
| Wild type (+/+) |
 Chestnut or sorrel |
 Bay |
 Black |
| Frame Overo (O/+) |
 Chestnut overo |
 Bay overo |
 Black overo |
| Lethal White Syndrome (O/O) |
 Lethal White Syndrome |
Lethal White Syndrome |
Lethal White Syndrome |