I'm working on a series of cat-inspired range trotters right now, and I kept getting stymied by the lack of anything resembling tabby stripes. Clearly the solution was just to invent a new gene. Enter the Tabby gene!
This gene is meant to cover any tabby pattern seen in domestic cats. (Please note this excludes Bengals and other exotic hybrids- those markings are already covered by preexisting genes.) What I've drawn out above are the main patterns, but they're intended as guidelines more than rules. If you'd find it on a tabby cat, it's covered by the Tabby gene.
TbTb/Tbtb: Tabby is a dilution gene that causes a variety of stripe patterns to appear on a horse's coat. These stripes resemble the various tabby patterns seen in domestic cats. Stripes are always a darker shade of the base coat. Additionally, Tabby causes a lightening effect on a horse's legs, underside, and muzzle. All Tabby horses will display dark ears, at least one stripe through the eye, a distinctive forehead 'M', and a white patch encompassing the lower jaw and upper throat.
(Thank you, tikki-tak, for letting me use your wonderful lines!)