Krista loves Tobias, her energetic and sometimes rambunctious two-year-old shelter dog, but often wonders what mix of breeds he is. “He looks like he may have beagle and collie in him, but it’s hard to say,” she says. “If I knew for sure, maybe I could better understand some of his quirks and what to do about them.”
Until recently, those with mixed dogs could only speculate about what breeds contributed to their companions’ genetic ancestry. But the ground-breaking development of two mixed breed DNA tests for dogs has removed the guesswork and now allows people to identify the combination and proportion of breeds in most dogs.
Unraveling the mystery
Humans have 23 pairs of chromosomes, but dogs have 40. The dog genome (the complete set of DNA contained in the 40 canine chromosomes) contains roughly 2.5 billion letters of the DNA alphabet, which spell out the instructions needed to make all the molecules, cells, tissues and organs dogs need to develop, live, grow, learn and play. Because dogs, like humans, each receive 50% of their genetic material from their mother and 50% from their father, genetic tests can identify certain patterns of DNA shared among close family members. In humans, as well as in dogs, these patterns can be used for applications such as paternity testing.
American Kennel Club (AKC) breeds are produced through closed breeding techniques, meaning only dogs derived from existing AKC breed members can be registered as members of that breed. This means that some patterns of DNA are shared between members of the same breed, but not between dogs from different breeds. So, in a sense, one can think of a dog breed as one huge inbred family; in fact two dogs from the same breed are genetically more closely related than two unrelated humans.
Adding to the mix
The new mixed breed genetic tests were developed by analyzing large numbers of AKC registered dogs from hundreds of different breeds, and identifying breed specific patterns of DNA spread across the 40 dog chromosomes. Once identified, these patterns can be detected using relatively small numbers of positions within the canine genome. Although there are actually billions of DNA letters in the dog genome, the breed tests use between 300 and 400 letters located at precise positions within the genome to assess a breed or breed mixture. These particular positions correspond to the regions of the canine genome that are most different (polymorphic) between different dog breeds.
Understanding the limits
It’s important to keep in mind that because these tests rely on patterns within the dog DNA to identify breeds, they may not be accurate for a dog with a large number of different breeds in his ancestry. To date, in fact, both available tests are 86% to 90% accurate only when validated on first generation cross-bred puppies produced from known parents of two different purebred breeds. Generally speaking, though, these tests are capable of identifying breeds that correspond to one grandparent (or possibly one half of one grandparent).
For example, consider a mixed breed dog that has four purebred grandparents:
Maternal grandmother – golden retriever
Maternal grandfather – German shepherd
Paternal grandmother – standard poodle
Paternal grandfather – boxer
This dog would be identified as a mix of those four breeds. However, the tests would likely fail to identify any breeds in a mixed dog whose grandparents were each equally mixed with four more different breeds (none of which were shared among the grandparents). That’s because the dog in question would be an equal mix of 16 different breeds – a combination that’s too dilute for detection. It’s worthwhile noting, however, that if the same dog had grandparents that were each one-quarter Labrador retriever, then he would be identified as containing that breed because the Labrador contribution from each grandparent would provide enough DNA for the tests to detect.
Advantages of testing
These DNA tests are designed for use in mixed breed dogs and not to assess whether a particular dog is purebred or not. Knowing the composition of a mixed breed can help you develop an appropriate diet, wellness plan and exercise routine for your dog. At present, the tests do not provide information about whether or not a dog will develop a breed specific disorder later in life; however, they can help you develop appropriate plans for screening your dog for any disorders associated with the breeds identified by the testing.
For example, disorders like osteosarcoma (bone tumor), which can occur in large and giant breeds, generally begin with swelling, pain and lameness, signs also indicative of many other disorders. Because mixed breed dogs may not resemble their breed composition, osteosarcoma may not be immediately considered. Knowing that a lame dog is predominantly one of the breeds susceptible to this disease may better facilitate diagnosis and treatment.
Though genetic testing won’t give you a detailed family tree of your beloved mutt, it can help you determine which breeds form the largest part of his makeup, and even lead to a better understanding of his individual behaviors and needs.
DNA Tests 1-2
Currently, there are two commercially available mixed breed genetic tests. Both are available through the companies offering them, although you will need to work with your veterinarian when a blood sample is required.
1. Mars Veterinary Wisdom Panel™ MX Test (whatsmydog.com) – can detect over 150 different AKC breeds and requires blood for the testing sample
2. Canine Heritage™ XL Breed Test (dog-dna.com) – can identify 100 breeds; this test utilizes cheek cells obtained from rubbing a soft brush against the dog’s inner cheek
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