A photograph of a dog at a veterinary hospital has gone viral this week because of the animal’s unusual but beautiful markings. The Labrador Retriever, Bull, has a coat colored like that of a calico cat. He is a patient at Texas A&M Veterinary Medical Teaching Hospital, according to MSN Now.

Because of Bull’s unique coat, he is suspected of being a chimera, a single animal that genetically is two animals, i.e., an individual that is its own twin. Bull, then, appears to be a chimera that is both black Lab and yellow Lab.

We saw this phenomenon last summer when a "two-faced" calico chimera cat named Venus caught the Internet’s attention. Bull has emerged as Venus’ canine counterpart, albeit without the same dead-even color split down the middle of his face.

Whether Bull is a chimera hasn’t been confirmed medically yet, but we’ll watch the veterinary hospital’s Facebook page to see if they post any further information and, hopefully, more photos of this interesting dog.


What is a chimera?

A chimera is typically formed from four parent cells (either two fertilized eggs, or two early embryos that have fused together).When the organism forms, the cells that had already begun to develop in the separate embryos keep their original phenotypes and appearances — resulting in a two-faced cat like Venus. (see second picture)

It can happen to humans too. In 1953 a human chimera was reported in the British Medical Journal. A woman was found to have blood containing two different blood types that apparently resulted from cells from her twin brother living in her body. Other such instances have been reported in the decade since.