Guess the Genotype #55

Can you guess this dog's genotype? Its breed?

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This is a Yorkshire terrier named Tootie. Yorkies change considerably from puppy to adult, and this is thanks to the two main genes controlling the breed's color.

This dog is saddled tan, a gene which appears to be fixed in the Yorkshire terrier breed. Saddled tan is known in part for its noticeable changes as a dog grows. At birth, saddled tan dogs will appear to be the same as tan pointed dogs. However, saddled dogs will have their black start to recede at a rather young age. Despite this, saddled and tan pointed dogs are genetically the same on the Agouti locus: atat black and tan. The differences between the two are caused by as of yet unknown modifiers.

The red on this dog is moderate, but the lightening of the color seems to come from the next gene I will discuss as all Yorkies are born rather dark. As such Tootie is probably genetically CC dark red.

Tootie is also gray, which is a very different color from blue. The two are often confused since they end up looking rather similar. However, blue and gray are very different. Blue is caused by a recessive dilution gene and all blue puppies are born blue. Also, the entire dog is affected, with the nose and eyes becoming diluted as well. In contrast, gray dogs will be born black (or the dilutions thereof as graying chocolate is known) and pale with age. Progressive graying is also believed to be a dominant gene, though unlike blue this is only theorized from breeding data. Unlike in blues, the dog's nose and eyes are unchanged, staying as dark as any black dog. These characteristics (pale gray coat with dark nose and eyes) can be seen in Tootie. Since it appears that the breed is fixed for this gene, Tootie must be GG gray.

So, that's atat CC GG or graying saddled tan.