A study conducted by researchers in the Purdue University College of Veterinary Medicine shows that some breeds of dogs have hidden coat colors and other traits. If you have a purebred dog, it’s likely that he or she looks fairly similar to other dogs of the same breed, especially when it comes to the color of their coats. But if a purebred puppy does not look exactly like its siblings when it’s born, chances are, it might not be a flaw – but rather a hidden gene variant that decided to show itself.
A research team led by Dr. Kari Ekenstedt, assistant professor of anatomy and genetics in the College’s Department of Basic Medical Sciences, and Dr. Dayna Dreger, the lead scientist in Dr. Ekenstedt’s canine genetics research laboratory, looked at a dozen different genes in 212 dog breeds. The Purdue researchers, together with industry partners at Wisdom Health, analyzed data that had been initially collected by WISDOM PANEL™ for the development of canine DNA tests. The work was published October 28 in PLOS ONE.
“These are purebred dogs with traits that their breed clubs say they’re not supposed to have,” said Dr. Ekenstedt, whose research program focuses on canine genetics. “The message of this paper is, ‘Hey, these gene variants exist in your breed, and if a few dogs are born with these traits, it’s not caused by accidental breeding and it’s not a mutt; it’s a purebred showing this known genetic potential.’”
Along with analyzing the data, researchers used standard breed descriptions from major American and international dog breed registries to determine coat colors and tail lengths that were accepted within each breed.
“There was a lot of information we didn’t expect,” Dr. Dreger said. “When it comes to different dog breeds, their standards are mostly based on preference and aesthetics. We make assumptions for certain breeds based on what we expect their coat colors to be.”
Dr. Ekenstedt explains that coat color genes have a significant amount of epistasis between them, meaning that what happens at one gene can mask what’s happening at another gene. Because of epistasis, it’s rare to see those masked genes actually expressed in a dog’s coat color.
One example of a “fault” allele – a gene variant that would cause a trait that is not allowed in a breed standard – is an allele that causes the color brown, which affects both hair pigment and skin pigment. The color is allowed in breeds like the Labrador Retriever where it causes the chocolate color. However, researchers observed that in breeds where brown is not allowed, such as the Rottweiler and the German Shepherd Dog, brown alleles exist at low frequencies.
Another example of a fault allele is in the Weimaraner, which exists in both long-haired and short-haired varieties. At least one dog breed organization does not allow long-haired Weimaraners, while several others do allow them. Of the Weimaraners sampled in this data, the long-haired allele is present at a 4% frequency.
The same goes for other traits, too, Dr. Dreger says. For example, around 18 recognized breeds of dogs have the genetic potential to be born without a tail – such as the popular Australian Shepherd. But the data shows that up to 48 of the breeds analyzed possess the tailless gene variant, usually at a very low frequency; one of those breeds is the Dachshund. “A breeder would certainly be surprised to see a Dachshund born without a tail,” Dr. Dreger said. “The chances are low, but our research shows that the potential is there.”
Both Drs. Dreger and Ekenstedt hope the research prompts some discussions within the dog community. “I want this to start science-based conversations,” Dr. Dreger said. “We’re not here to make decisions on what a breed should or shouldn’t look like or what a breed club should do. We’re here to say these are the facts, and these are the gene variants that naturally exist in these breeds.”
They also hope the study changes some perspectives when it comes to what is to be expected with certain breeds of dogs. “There’s an assumption that the standards for these different breeds of dogs are set in stone,” Dr. Dreger said. “People will often make assumptions that if it doesn’t match this, it’s not purebred. This data shows that there is a lot of variation in some of these breeds, and the standards are not as concrete as we expect them to be.”
Wisdom Health funded a Veterinary Summer Scholar position related to the study for Blair Hooser, a Purdue veterinary student in the DVM Class of 2021 and co-author on the paper. Partial support for Dr. Ekenstedt was provided by the National Institutes of Health.
You can read True Colors: Commercially-acquired morphological genotypes reveal hidden allele variation among dog breeds, informing both trait ancestry and breed potential at PLOS ONE.