Roof Rat born with split tail: is it genetic?

She is otherwise normal, friendly and healthy

She was one of a litter of 5 babies. The rest were apparently normal.

She was one of a litter of 5 babies. The rest were apparently normal.
Until recently, nearly all pet rats were Norway Rats (Rattus Norvegicus.) Also known as “Fancy Rats”, these were sold in pet stores, bred by breeders and even used in