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Paint and Pinto Genetics: Overo, Spalshed White, and Sabino

Overo

Overo covers at least three alleles of three different genes, each of which creates a distinct color pattern. As with tobiano, the overo alleles are dominant and can hide alleles for solid color.

FrameThe frame allele produces horses that are white across the sides of the body and have a great deal of white on the head. A show-quality frame horse will look as if the white is inside a picture frame of dark areas along the top line and belly. The edges of the spots tend to be jagged. Many have a dark mustache on the upper lip. Sometimes a frame horse will be solid colored except for a bald face.

Regardless of whether a frame horse has only a bald face or is almost all white, it will reproduce about the same. If bred to a solid color horse, at least half the offspring will be spotted.If you breed a frame mare to a frame stallion, you have a 25% chance of getting a homozygous frame foal. These are solid white. Within days of birth, they always die of the lethal white syndrome. However, if you breed frame to non-frame, you will never get a lethal white foal.

You cannot tell for sure whether a horse carries the frame allele just by looking. The genetic test for frame costs only $50 for the first horse plus $25 for any additional ones you wish to test.

Splashed White

Splashed white is caused by six alleles in two different genes. These.alleles are rare, but becoming more common in the Paint registry. Matings in which both the dam and sire variously have any of these alleles should produce all splashed white offspring.

A splashed white horse looks as if you dipped it feet first into a can of white paint. It will have white legs and belly and a mostly white head, but be dark above. This contrasts with Tobianos, who have white legs and a dark head, and other overos, which have a lot of white on the head, yet dark legs.

Splashed white horses can throw healthy solid white foals. There is evidence that the solid white offspring of splashed white parents are homozygous and will always throw spotted foals when bred to solid-colored horses.

Deafness is common among splashed white horses. However, the majority are normal. There is no test to rule out transmission of deafness.

Warning: According to researchers, you may have trouble getting foals from mating splashed white horses with each other, as some combinations kill the embryo early in gestation.

 

Note the colt's dark "mustache," the white on the side of his body, blue eyes, and lack of white on his legs. Although his white follows the Frame pattern, only genetic testing can confirm this.

The same colt, side view.

Sabino

The remaining overos are classified as sabino. Scientists suspect that sabino may be a mixture of superficially similar patterns carried by several alleles of perhaps more than one gene. Sabino is a dominant trait.

A sabino can produce healthy solid white foals. Other possibilities include white with speckles, Medicine Hat (dark ears and the rest of the body almost entirely white), vertical streaks and bands, or a pattern that is almost the same as frame. Areas of roan are common.

There is a test for homozygosity. It is worth testing as even nearly solid white sabinos, if heterozygous, can occasionally produce foals that can be registered only as "breeding stock." If both dam and sire are homozygous, all offspring will be at least 90% white.

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