Contract & Guarantee

 Understanding the Limitations of Canine DNA Ancestry Testing  

By Patricia Duffer - Used with permission

DNA testing is an incredibly useful tool for breeders and dog owners, but not every part of a DNA test works the same way. One of the most commonly misunderstood is breed ancestry.  

An ancestry test does not actually determine whether a dog is purebred. There is no single “Chihuahua gene” that identifies a dog as a Chihuahua. Instead, the testing company compares the dog’s DNA with groups of dogs in its database and looks for the closest genetic matches.  

This works best when the company’s database includes a large and diverse representation of the breed.  

That becomes important with import lines.  

Chihuahuas have been bred throughout the world, often within relatively separate populations for many generations. Import lines may carry genetic patterns that are not as well represented in a testing company’s database. When the computer cannot closely match part of a dog’s DNA to the Chihuahuas in its reference population, it may assign that DNA to another breed with similar genetic patterns.  

Sometimes that difference can be substantial.  

This does not automatically mean another breed appears in the dog’s recent pedigree. The test is reporting the closest genetic match available within its reference database, and the accuracy of that estimate depends partly on which bloodlines and populations are represented there.  

This limitation applies specifically to breed ancestry estimates. It does not make the genetic health portion of the test unreliable. Health testing looks for specific genetic variants associated with particular conditions rather than estimating breed ancestry by comparing a dog to reference populations.  

As DNA companies add more dogs and more diverse bloodlines to their databases, ancestry estimates can also change. The dog’s DNA hasn’t changed—the information available to interpret it has.  

DNA ancestry testing can provide valuable information, but an ancestry percentage should be understood for what it is: an estimate based on the reference populations available at the time of testing, not a genetic certification of purebred status. 

In short, if a dog looks like a purebred Chihuahua, has documented lineage confirming it, and the only doubt comes from a genetic test result, especially if it’s from an imported line, its purebred status shouldn’t be questioned. Science is always evolving. - Patricia Duffer, Midwest Working Chihuahuas