DeNise explains it this way: “In a population of any breed, there are dogs that are carriers but don’t exhibit phenotype [observable characteristics]. If you reduce the size of breeding population—creating what we call a bottleneck—you start increasing the frequency of deleterious traits, like dwarfism or white coat. If we looked at the DNA of, for instance, a group of white mini-German Shepherds, they would probably cluster with German Shepherds. After they’ve intermated for five to six generations, we may not come up with that. They would cluster with each other. If breeders were changing allele frequencies quickly, you could do it very fast.
“There are always contradictions that make you say, ‘Huh, that’s really weird.’ One odd thing that happens is due to some sort of random assortment of genes in mixed-breed dogs. The algorithm may identify a breed that is not consistent with the physical appearance of the dog. We sometimes get an indication of this when the certificate is printed with the picture of the dog provided by the owner, and the certificate is reviewed by our customer service department prior to mailing it to the pet owner.”
A 90-pound, wiry-haired mongrel who swims, chases balls and makes goo-goo eyes like a Golden Retriever and whose only pedigreed relative is a very distant Chihuahua confounds the process, but says a whole lot about the complexity of canine genetics and why some scientists devote their careers to studying canine evolution. Extreme variation in anatomy and behavior is unique to the domestic dog. If humans were an equally anomalous species, we’d weigh between 20 and 650 pounds and range in height from three to 10 feet. In dogs, adaptations change with such speed that scientists suspect there may be a clue in the canine genome that could reveal how evolution works.
Sorting It Out
Before they launched the project, MMI tested DNA from a street dog rescued from a Thai village. You’d think there would be no clusters of any kind, but the computer identified Chow and Akita in the mix. This isn’t surprising, because the free-living common village cur who populates most of the developing world may be the closest living relative to the original proto-breed. Findings suggest that Thai pooch stores a sizable chunk of the original genetic blueprint of every single living dog in her DNA. The question is, how much?
MMI can’t as yet define the percentage of “breedness” in mixed-breed dogs. One reason is that some breeds cluster loose and others tight. Why this happens isn’t clearly understood. German Shepherds, Standard Poodles and Collies cluster tight. Miniature Poodles cluster tight, but Toy Poodles cluster loose. Within their breeds, Labrador Retrievers and Beagles often cluster as two different groups. According to DeNise, “Labs from the United Kennel Club that are bred specifically for hunting and AKC Labs do not necessarily cluster as one breed. And AKC Beagles and Beagles bred specifically for research don’t cluster together either.”
She adds, “In my opinion, it’s possible that a population that increases rapidly doesn’t cluster as well as those populations that have remained static. This is because, as you increase a population to accommodate breed popularity, people breed everything, including animals that may not exhibit all the physical characteristics that are desirable.”
And even when dogs look alike, they can display behavioral differences. As DeNise notes, “We understand so little about how behaviors are coded. Many behaviors are learned, but there are probably multiple genes that are responsible for herding, birding, heeling—these kind of hard-wired behaviors.”
Scientists are eager to tease out genetic connections to breed-associated motor patterns. When wolves hunt, they display these behaviors sequentially: orient > eye > stalk > chase > grab-bite > kill-bite > eat. Artificial selection, however, extracts and segregates these patterns in incomplete sequences. In certain breeds, individuals perform the abbreviated motor pattern repeatedly. A Pointer who stops dead in her tracks and stands stock still with her front leg held rigid in mid-stride to indicate the presence and position of game is the lofty goal of bird-dog breeders. To wolves, it’s just a good meal interrupted.