Overo

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The frame overo colour pattern consists of any basic horse colour (brown, black, bay, etc.) and irregular white usually vertical spots. The spots are often irregular, jagged.

White rarely crosses the back and the base colour creates the so-called frame of the horse. The lower legs and feet tend to be dark although white spots with white feet may occur. Tail is single-coloured, usually dark. The head is often white or bald-faced and blue eyes are not uncommon.

The O allele causing frame overo colour pattern is autosomally dominant. Frame overo is a colour pattern with most frequent occurrence of the lethal genetic disorder called Overo Lethal White Syndrome. These are homozygous OO Overo foals, which die soon after birth due to abnormalities of their alimentary tract. Heterozygous foals (ON) survive and these then become frame overo.

Table of carrying the O allele: