Frame overo - sekelsta/horse-colors GitHub Wiki

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.

Frame Overo Gene

	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