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. There is disagreement regarding the exact history of the breed prior to its arrival in the United States, and thus no official consensus on the origin of its name or association with Australia. These dogs usually have a mostly white coat and blue irises, and are often deaf, blind, or both. In this case, the deafness and blindness are linked to having two copies of the merle gene, which disrupts pigmentation and produces these health defects. The shepherd should be brushed weekly to maintain a healthy and clean coat and also to prevent matting. Being a 'working dog', this breed should be outside to get its needed exercise. If a dog is dirty, a basic bath can be given, but not frequently, for it can dry out the skin and coat.