Eel stripe

Primitive markings are a group of hair coat markings and qualities seen in several equine species, including horses, donkeys, and asses. In horses, they are associated with primitive breeds, though not limited to such breeds. The markings are particularly associated with the dun coat color family. All dun horses possess at least the dorsal stripe, but the presence of the other primitive markings varies. Other common markings may include horizontal striping on the legs, transverse striping across the shoulders, and lighter guard hairs along the edges of a dark mane and tail.

The dun coat and attendant primitive or "dun factor" markings reflect the wild type coat and are observed in all equine species. Cave paintings depict horses as being dun and with the primitive markings. The last remaining true wild horse, Przewalski's horse, is also dun-colored with primitive markings. So, too, are horse breeds such as the Konik and the Heck horse, "bred back" to resemble the now-extinct tarpan, many of which are grullo or mouse dun in color.

While no dun horse is without a dorsal stripe, primitive markings also sometimes occur on horses of other colors, particularly those with sooty characteristics and newborn foals. Primitive markings in horses are an example of atavism: preservation of or reversion to ancestral type. While primitive markings are closely linked with the dun coat colors, the variations of expression and presence in non-dun horses suggest that the markings themselves may be governed by a separate genetic mechanism.

Of equids other than horses, all except the mountain zebra show a distinct dorsal stripe. Among domesticated donkeys, most have a black dorsal stripe, though it can be difficult to see on melanistic individuals. In the African wild ass, the dorsal stripe is thin but distinct and black. In Przewalski's horse, the dorsal stripe is usually dark brown, while it is black in the bred-back tarpan. In the plains zebra, the dorsal stripe is narrow and edged by white, while in Grevy's zebra, it is quite bold. The dorsal stripes of the onager and kiang are dark brown and especially vivid.

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