Dun and d1 (nd1)
The dun coat colour in horses dilutes both red and black pigment by limiting the distribution of pigment granules to a small part of the hair shaft. This dilution is accompanied by darker undiluted markings that can include a dorsal stripe (most commonly), leg barring, dark ear tips, and shoulder bars. The face and points of dun horses are also usually darker than their bodies.
The coat colour and markings associated with d1 (also called nd1) are less intense than dun, but follow the same pattern. Horses that are positive for d1 but not dun are NOT considered to be dun.
Gene or region and technical reference
Gene: TBX3 (causative). Reference: Imsland et al. (2016)
n. Test developed using manufactured DNA, animal controls.
D. Test developed using manufactured DNA, animal cases.
d1. Test developed using manufactured DNA, animal cases.
Miniature horse stallion Silver Star King Of Cool shows us his dorsal stripe and mane frosting. He is a splashed white dunskin.