One of the world's most famous cryptids is the so-called blue tiger, first sighted in China a century ago. Cryptozoologists have even worked how such a creature might come to be. Here are the real genetics of a (probably) fake animal.
The blue tiger, or maltese tiger, came to international attention in 1910, when a missionary in the Fujian province of China noticed what he thought was a man in a blue suit. It turned out to be a tiger with a smoky blue coat striped with black. Understandably, few people took the word of a guy who, at first, mixed up a person and a big cat, but eventually the word, and the promise of a reward, got out and hunters got involved. There were some breathless accounts of near-captures, but no one ever managed to get the cat.
There still are breathless accounts of the maltese tiger. Stories turn up, from time to time. Some people claim a blue-tinted cub was born at the Oklahoma Zoo in 1964. The cub was killed in infancy by its mother, but pictures of the preserved animal show an unmistakably orange cub in a specimen jar with a darkness about its sides that could be shadows or could be a slight gray tint to the fur.
The Genetics of a Cryptid
Cryptid aficionados have theories as to how these tigers might be produced. Tigers have the agouti gene, a gene that determines whether animals - from dogs to horses, have patterned fur. It causes a range of pigmentation patterns in dogs and cats, as well as the darkening that is sometimes seen around the ears and lower legs of horses. One of the products of the agouti gene is the agouti signalling peptide. In mice, the presence of this peptide causes melanocytes - the pigment producing cells which would usually produce brown or black pigments - to suddenly start manufacturing the orange or yellow pheomelanin pigments.
In domesticated animals, especially cats, there is also the dilution gene. This fades out the normal color, and produces the gray, and sometimes faintly blue, color that we sometimes see in cats. A maltese tiger, would have to have a combination of the agouti gene with the dilution gene. The agouti gene would give the tiger stripes, but the dilute gene would wash out the orange and turn it gray.
Tigers are relatively variable in their colors. There are pure white tigers with barely distinguishable stripes, white tigers with black stripes, and golden tigers that have slightly deeper gold stripes on a tawny background. Reports of black tigers or gray tigers still do turn up. Despite the stories told by hunters and the brief glimpses of hikers or farmers, it's doubtful that this kind of cat exists. It would be nice to see one, though. From a distance.