The Australian Shepherd, often known simply as the 'Aussie', is a medium-sized breed of dog that was, despite its name, developed on ranches in the United States during the 19th century. Also, great variety is seen in the Aussie's eye color, and they are often heterochromatic. An early nickname for the breed was 'ghost-eye dog'. Aussie eyes may be any shade of brown, or blue; they may have two differently colored eyes, or even have bicolored or 'split eyes' (for example, a half-brown, half-blue eye), which appear to be linked to the merle coloration. The merle phenotype in Australian Shepherds is very similar to the coat color in Mitf mouse mutants. Other conditions of note include iris coloboma, canine hip dysplasia, Pelger-Huet anomaly, hypothyroidism, and nasal solar dermatitis. Prior to breeding, the Aussie should be checked for hip and elbow dysplasia and DNA tests performed to show the dog to be free of the MDR1 mutation, cataract mutation, and CEA.