On polycerate animals it is preferred that there is a fleshy gap between the two pairs of horns. Partial or deformed horns that are not firmly attached to the skull, often referred to as "scurs", are not unusual but are considered undesirable. Markings Each Jacob has distinctive markings that enable the shepherd to identify specific sheep from a distance. Desirable colour traits include an animal which is approximately 60% white, with the remaining 40% consisting of a random pattern of black or "lilac" (brownish-gray) spots or patches. The skin beneath the white fleece is pink, while skin beneath coloured spots is darkly pigmented. Both rams and ewes exhibit black markings, some of which are breed specific and some of which are random. Breed specific markings include large, symmetrical dark patches incorporating the ears, eyes and cheeks, and a dark cape over the dorsal part of the neck and shoulders. The face should have a white blaze extending from the poll to the muzzle. The muzzle itself should be dark. The classic Jacob face is often referred to as "badger-faced", consisting of black cheeks and muzzle with a white blaze running down the front of the face. In addition to these markings, random spots may occur on the rest of the body and legs (including the carpi, hocks, and pasterns). Certain markings are common in particular lines: large muzzle markings, lack of leg markings, lack of muzzle markings, etc. The lilac color is caused by a recessive variant of the MLPH gene. Diseases Several rare or unusual diseases have been identified in Jacob sheep. The condition known as split eyelid is a congenital defect common to several polycerate British breeds, and is genetically linked to the multi-horned trait. In mild cases, the eyelid shows a "peak" but does not impair vision or cause discomfort. Extreme cases (Grade 3 or higher) result in a complete separation of the upper eyelid in the middle. In 1994, an unusual form of asymmetric occipital condylar dysplasia was found in two Jacob lambs; a possible link to the multi-horn trait has been suggested. In 2008, researchers in Texas identified the hexosaminidase A deficiency known in humans as Tay–Sachs disease in four Jacob lambs. Subsequent testing found some fifty carriers of the genetic defect among Jacobs in the United States. The discovery offers hope of a possible pathway to effective treatment in humans. Husbandry The Jacob is