Overo

Overo refers to several genetically unrelated pinto coloration patterns of white-over-dark body markings in horses, and is a term used by the American Paint Horse Association to classify a set of pinto patterns that are not tobiano. Overo is a Spanish word, originally meaning "like an egg".^[1] The most common usage refers to frame overo, but splashed white and sabino are also considered "overo".^[2][3] A horse with both tobiano and overo patterns is called tovero.

Frame overo, splashed white, and sabino are three separate pinto patterns, genetically unrelated, that are grouped together under the name "overo".

The frame overo pattern tends to have white spots on the flanks and face, surrounded by a dark "frame" of color. If two horses with the frame overo gene are bred together, there is a 25% chance the foal will have lethal white syndrome.^[4]

Splashed white or splash overo is a group of patterns that tend to have white on the underside, as if a horse ran through white paint with its head lowered. So far 6 alleles on two genes have been discovered to cause splashed white patterns. There is a correlation between the splashed white pattern and deafness.^[5]

Sabino or sabino overo is a group of patterns that typically have white on the legs, face, and sometimes also belly, often with white ticking or roaning. Several alleles on the KIT gene are known to cause sabino or sabino-like patterns.^[6][7]