CANINE BREED TESTING
Owners interested in learning the breed makeup of their mixed-breed pets can now use genetic testing to find out this information. Although owners can obtain these results without consulting you, it is beneficial for you to understand the science behind these tests to answer clients' questions and realize the limitations of these tests.
The unique genetic signatures of many dog breeds have been identified. A single nucleotide polymorphism (SNP) is one such signature. A SNP is simply the change of a single nucleotide to another in the DNA sequence and can occur anywhere in the genome. As dogs are selectively bred over time, specific SNPs can become concentrated in that breed. For example, a SNP may be located close to a gene involved in curly hair. As dogs are selectively bred for curly hair, that closely linked SNP is also inadvertently selected. If a SNP or certain combination of SNPs is present in a certain dog breed and not in other breeds, it can be used as a marker for identifying that breed through DNA analysis. To identify its parental breeds, a mixed-breed dog's DNA can be analyzed for these SNPs and then compared with known purebred SNP profiles (Figure 4). For example, if a dog has a large percentage of SNP combinations found mainly in boxers, then it most likely has a boxer in its pedigree. If this same dog also has several SNPs common to beagles, then it likely has a beagle relative, as well.
Canine breed identification is available from numerous companies for less than $100 a sample. Most companies will send the test kit directly to the pet owner, and the DNA sample is collected using a cheek swab. The exception is the Wisdom Panel Professional (Mars Incorporated), which analyzes a large number of breeds using numerous SNPs and requires a sample of whole blood.11 The number of SNPs analyzed varies by company, and, in general, the more SNPs analyzed, the higher the accuracy of the test results. Perhaps of secondary importance is the number of breeds included in the analysis, as several providers state that about 62 breeds contribute to 92% of the genetics in the U.S. dog population.12-14
While the main interest in this testing may be to satisfy owner curiosity, it does have value to practitioners. Preventive care can be better tailored with knowledge of a pet's pedigree. Although breed typing cannot truly be associated with inherited disease risk, it can serve as a starting place. An example of testing's potential value is that a primarily boxer-mixed dog would be at higher risk of carrying the autosomal dominant mutation for arrhythmogenic right ventricular cardiomyopathy. Insight into this pedigree would give the owners the option to test directly for the STRN mutation, the causative gene in arrhythmogenic right ventricular cardiomyopathy, and to consider more in-depth cardiac monitoring for their pets.
Both genetics and environment determine behavior, and pedigree typing is not considered an accurate method to assess temperament or predict most behaviors in mixed-breed dogs. However, studies have found that a limited list of behaviors including territorial defense, playfulness, and excitability have a strong genetic component independent of environmental influences, suggesting that knowledge of a dog's pedigree may be helpful in better anticipating and managing these specific behaviors.15