Ear and Body type thumb|right|A male Dumbo rat, a variety with ears placed lower on the head Two of the most prominent and standardized physical changes applied to rats through selective breeding are the development of the Manx rat and Dumbo rat. The Dumbo rat, whose origins are in the United States, is characterized by having large, low, round ears on the sides of its head, versus the smaller and less prominent ears seen on a standard eared rat. Dumbo ears are caused by a recessive mutation, and was named for its resemblance to the fictional character Dumbo the Flying Elephant. The Manx rat is tailless due to a genetic mutation, and was named for the Manx cat which shares this feature, though not necessarily due to the same mutation. Breeding Manx rats does raise some ethical and health concerns however, as rats use their tails for both balance and thermoregulation.
Ear and Body type thumb|right|A male Dumbo rat, a variety with ears placed lower on the head Two of the most prominent and standardized physical changes applied to rats through selective breeding are the development of the Manx rat and Dumbo rat. The Dumbo rat, whose origins are in the United States, is characterized by having large, low, round ears on the sides of its head, versus the smaller and less prominent ears seen on a standard eared rat. Dumbo ears are caused by a recessive mutation, and was named for its resemblance to the fictional character Dumbo the Flying Elephant. The Manx rat is tailless due to a genetic mutation, and was named for the Manx cat which shares this feature, though not necessarily due to the same mutation. Breeding Manx rats does raise some ethical and health concerns however, as rats use their tails for both balance and thermoregulation