Breeding of different branches of the equine family, which does not occur in the wild, generally results in sterile offspring.

[citation needed] Like mules and hinnies, however, they are generally genetically unable to breed, due to an odd number of chromosomes disrupting meiosis.

This provoked the interest of Cossar Ewart, Professor of Natural History at Edinburgh (1882-1927) and a keen geneticist.

Ewart crossed a zebra stallion with pony mares to investigate the theory of telegony, or paternal impression.

In The Origin of Species (1859), Charles Darwin mentioned four colored drawings of hybrids between the ass and zebra.

He also wrote In Lord Morton's famous hybrid from a chestnut mare and male quagga, the hybrid, and even the pure offspring subsequently produced from the mare by a black Arabian sire, were much more plainly barred across the legs than is even the pure quagga.

[15] In his book The Variation of Animals and Plants Under Domestication, Darwin described a hybrid ass-zebra specimen in the British Museum as being dappled on its flanks.

During the South African War, the Boers crossed Chapman's zebras with ponies to produce animals for transport work, chiefly for hauling guns.

A specimen was captured by British forces, presented to King Edward VII by Lord Kitchener and photographed by W. S.

Zorses were bred by the U.S. government and reported in Genetics in Relation to Agriculture by E. B. Babcock and R. E. Clausen (early 20th century), in an attempt to investigate inheritance and telegony.

In the 1970s, the Colchester Zoo in England bred zedonks, at first by accident and later to create a disease-resistant riding and draft animal.

Today, various zebroids are bred as riding and draft animals and as curiosities in circuses and smaller zoos.

A zorse (more accurately a zony) was born at Eden Ostrich World, Cumbria, England, in 2001, after a zebra was left in a field with a Shetland pony.

Usually, a zebra stallion is paired with a horse mare or donkey jenny, but in 2005, a Burchell's zebra mare named Allison produced a zonkey called Alex, sired by a donkey jack at Highland Plantation in the parish of Saint Thomas, Barbados.

[19] In 2007, a horse stallion, Ulysses, and a zebra mare, Eclipse, produced a hebra named Eclyse, displaying an unusually patchy color coating.

[24] Khumba, the offspring of a zebra mare and a dwarf albino[broken anchor] donkey jack, was born on 21 April 2014 in the zoo of Reynosa in the state of Tamaulipas, Mexico.

[25][26] More recently, in November 2018 at a farm in Somerset, a cross between a donkey jack and a zebra mare was born.