Genetics 401

Dog Genetics – Level 4

Dog DNA Testing

Unraveling Mixed-Breed Mystery Mutts with DNA Tests
By Eve Adamson

It sounds too good to be true — can a simple test can tell you exactly what purebreds make up your lovable mixed-breed mutt? You’ve always wondered, speculated, even told others what you think your dog is. You’ve examined his eyes, ears, tail, and coat and compared him to purebred dogs you’ve seen. You hesitate whenever someone asks, “What kind of dog is that?” Is it true that you can really know for sure?

In 2005, when geneticists first completed a full genome sequence of a Boxer — a picture of all the dog’s genetic material — scientists realized what they could do with that kind of information. They went on to sequence other breeds, revealing to the world the genetic picture of a dog and all the minute genetic variations that distinguish dogs from, say, humans or mice, and also the variations that distinguish breeds from one another. Carrying the sequencing a few steps further, scientists could find genetic variations that seemed to trigger genetic diseases within a breed. Some of this information even translates to humans, since dogs and humans share many genetic diseases. Find the genetic mutation in the dog and it’s easier to find it in the human, helping researchers develop cures for both human and canine diseases. Dog breeders can also use DNA tests to verify paternity.

The reason geneticists can tell a Boxer from a Briard is tiny differences between the nucleotide sequences at specific locations in the genome. Some of these variations are called SNPs, or single nucleotide polymorphisms — signs of a genetic variation that may or may not show on the surface of the dog. While there is no one variation unique to any single breed, there are ranges of variations for particular breeds that help genetically distinguish a Golden Retriever from a Gordon Setter. But how does a dog genome tell you whether your mixed-breed dog has any Rottweiler or Chihuahua or Poodle in his blood?
Several companies have taken the information gleaned from the dog genome to create genetic databases of purebred dogs using autosomal DNA markers, which are inherited from both parents. After creating DNA profiles of particular breeds, they then engineer complex computer programs that can scan a dog’s DNA and compare it to DNA sequences of purebred dogs in their database. Results show which breeds the tested dog is most closely related to and which breeds are probably further back in his family tree.

Phenotype versus genotype
Creating these tests is a complex and expensive process. For their Wisdom Panel test, Mars Veterinary tested more than 4,600 SNPs from all over the canine autosomal genome using DNA from more than 3,200 dogs, then further refined results by determining the best 1,536 genetic variations between breeds, running those results against an additional 4,400 purebred dogs. The results created a panel of DNA markers from which Mars Veterinary created their database of over 225 breeds.

Creating such a database is no easy feat. It is expensive and time-consuming, and also requires maintenance, says Jim Simpson, president of BioPet Vet Lab. “We run a plate daily on a known purebred to ensure accuracy,” Simpson says.
Although the tests are not designed to determine breed purity, a purebred dog will get a purebred result about 90 percent of the time. (Dogs with a mutation or from another country with a bloodline not common in the United States may not have accurate results.) Test a mixed-breed dog, and the results will show a list of related breeds, limited only to that company’s breed database.

How accurate are the results?
“It’s hard to talk about accuracy when you are testing unknowns,” Simpson says. “We gauge accuracy by our complaint rate, which is very low.”

However, if a dog is primarily a breed not in the company’s database, the results will be less informative. For example, some companies do not include the American Staffordshire Terrier in their database, so if a Pit Bull mix is tested, the results will show the breeds most closely related to those — perhaps a Boston Terrier, even if the tested dog looks nothing like that breed. If, however, the dog is a Labrador Retriever mix or a German Shepherd mix (both common mixes), the results will likely be more illuminating. If the dog’s parents and grandparents were all mixed breeds, the results may be diffuse, with no breed standing out as dominant.

That doesn’t mean the results will explain a dog’s physical features, however. Many people are surprised that the list of dogs comprising their mixed-breed dog don’t resemble their dog at all. “A lot of folks have a preconceived notion of what their dog’s makeup is, and if the results don’t match that preconception, they may feel the results are not correct,” Simpson says. “That’s why we try to help people by guiding them to breed information so they can learn more and possibly discover that there is more to a breed than appearance.”  

As Mars Veterinary explains it, the genes determining phenotype (the physical characteristics of a dog as opposed to the genetic ones, or genotype) are of a very small number, and having a particular breed in a dog’s ancestry certainly doesn’t guarantee that the dog will have those same traits. When breeds mix, physical traits like erect ears, wiry coats, or curly tails can change or disappear. It all depends on how far back in the family tree a purebred is in relation to the tested dog. In addition, some traits are genetically dominant and some are recessive. Dominant traits are more likely to be passed along, but phenotype and genotype are complexly related. Still, getting the results can be fun and exciting, and could even shed some light on a dog’s behavior or genetic disease risk, since purebred dogs tend to have predictable behaviors and health tendencies.

How does it work?
Taking the test requires getting a cheek swab sample from the dog. The company sends a test kit with detailed instructions. Rub the swab on the inside of your dog’s cheek as directed, let it air dry without contaminating the swab (which could affect results), then send it back to the laboratory. In a month or two, you will receive the breed report. Mars Veterinary also has a blood test, which they claim is more accurate than a cheek swab test and draws from a larger database of breeds, but it must be purchased through and administered by a veterinarian. Mars recommends doing this during the dog’s regular annual exam, when the veterinarian may already be drawing blood for other tests.

Three major companies produce the tests (many other companies resell these tests). Before investing in a test, check the company’s website for the current list of breeds in the database, price, and instructions. The three major tests are:

  • BioPet Vet Lab DNA Breed Identification test, now marketed under the PetSafe brand as the PetSafe Breed Identification Dog DNA Kit: 63 breeds in the database; cost $59.95;
  • Canine Heritage Breed Test by MetaMorphix: 105 breeds in the database, cost $55.00 for a breed test taken from a 38-breed database or $79.95 for a test taken from the 105-breed database, which requires taking the first test previously.
  • Mars Veterinary Wisdom Panel Mixed Breed Analysis test: $69.99 for the Wisdom Panel Insights cheek swab test with a database of more than 185 breeds. Mars Veterinary also sells a Wisdom Panel Professional blood test through veterinarians, with a database of more than 225 breeds — the gold standard, but more expensive (ask your veterinarian about price).

Whichever test you might decide to try, remember that the results aren’t guaranteed, but they are likely more informative than a shelter worker’s or even a veterinarian’s guess. To many pet owners, knowing just a little bit more about their beloved mystery mutt is well worth the price

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