Wednesday, April 25, 2012

Guess the Genotype #66

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

Image from Wikimedia Commons under a Creative Commons license

This puppy is an Australian shepherd and is, in fact, a double merle. The dog is also deaf and, judging by the look of the eyes, has reduced vision as well. According to the image's description, both eyes have abnormalities. In addition to starburst pupils in both eyes, the dog's left eye also has an eccentric or drop pupil. Starburst pupils are known to cause moderate to severe light sensitivity, and eccentric pupils likely result in similar issues to a lazy eye or crossed eyes, since the pupil is always looking in a different direction from the normally placed pupil. Abnormalities such as these occur quite frequently in double merles when compared to other dogs. Other indications that this dog is a double merle is the majority of white in the coat--particularly on the face--and the loss of pigment to the nose. Now, on to the dog's genotype.

Since there is so little actual color on this dog, there is only so much that can be determined about its genotype. However, by looking at what color can be seen and also knowing color frequency in the breed, some conclusions can be made. First, this dog has black pigment in the few places where color shows. Since the most common genotype involving black pigment in the breed is tan point, I can be pretty confident that this dog is most likely atat tan pointed. However, since there is white where the normal distribution of tan in a tan pointed dog would be, there would be no way to be sure without knowledge of the dog's parentage or genetic color testing.

Next, the dog is a double merle, as I mentioned before. As the name implies, double merles have two copies of the merle gene. Whereas one copy of the merle gene leads to black in a coat appearing as if it had been splashed with bleach, two copies takes it even further., stripping pigment from sections of coat that would otherwise have color. This loss of pigment is why so many double merles are partially or completely deaf, due to loss of cochlear pigment. In a similar vain, it appears the gene interferes with proper eye development, causing all of the numerous abnormalities seen in double merles. This dog must be MM merle.

Last, but not least, it is likely that this dog is also Irish white under the homozygous merle. As with the tan point gene, Irish white is the most common form of the Spotting gene seen in the breed. As such, despite the fact that this dog most resembles an extreme white piebald, it is likely that genetically the dog is sisi Irish white.

So, that's atat MM sisi or double merle tricolor.


  1. it's so sad that people will breed dogs like this knowing the possible side effects :(

  2. The breeder probably didn't know this double gene would happen. It is probably a very unlikely event.

    1. Crossing two normal merles (Mm) always and forever means each of the puppies has a 25% chance of being double merle.