DNA tests started out as a fun way to try to figure out a mixed-breed dog’s genetic makeup. Many people I know who’ve done them have gotten results that made me a little skeptical — high percentages of extremely rare breeds. I am not a geneticist, though, and it all seemed harmless enough.

But.

People are using — and the testing companies are marketing — these tests in two ways that could be very, very bad for dogs: to attempt to predict dogs’ future health problems and to “tailor” behavioral training. And, according to an excellent column in Nature, the tests are extremely inaccurate.

Let’s start with the problem of trying to tailor behavioral training to the supposed mix of breeds in your dog. Your dog is a unique individual. Whether purebred or mixed, each dog’s behavior is affected to some extent by genetic drives — some dogs want to herd everything; some want to chase whatever moves. It’s also enormously affected by personality and experience. Within a breed, within a litter, even, the personalities and drives can be very different.

A good trainer tailors her teaching to the individual dog, of course, but she bases her work on the dog in front of her — not on some possibly wildly inaccurate list of breed percentages. If a dog is half Lab and half German shepherd, do you reward with food half the time, since the shepherd half might not be food focused? Do you use harsher methods half the time if your dog’s ancestry might lie in a military dog line? It’s silly when you start to parse out what it might mean in day-to-day training and life. A smart dog owner will choose a trainer who uses motivational methods tailored to the dog based on her hands-on experience working with that dog.

But a far more dangerous use of these tests is in attempting to predict future illnesses. The Nature article, and these related articles in the Washington Post and the Undark website explain the problems with this in great detail. In sum:

• The mapping of a single gene mutation to a specific disease is far from foolproof. Genes express themselves differently in different breeds, so a gene that is linked to a condition in one breed might not behave the same way in another breed. And no one really knows what happens in mixed-breed dogs.
• Having a specific gene mutation might (or might not) increase the risk of a particular disease. Basing a decision to euthanize your dog on very imprecise data, rather than on the actual dog’s health and symptoms, is cruel.
• People unnecessarily panic when they get the results that show gene mutations — which might be completely meaningless. They pay for — and subject their dogs to — unnecessary, stressful, and expensive tests, which generally don’t tell them anything conclusive anyhow.

The truth is, genetic testing in humans works much the same way … results are often highly inaccurate; they are not predictive; and they could cause people to panic and get unnecessary “treatment” for a disease they think they might get some day. But as an adult, you get to make that choice for yourself. Subjecting your dog to it — or killing him out of fear of what might happen — is horrible!

The testing companies are businesses. They make money by selling you the tests. They also make money by selling the huge amounts of data they collect on test subjects. Veterinary clinics are also businesses, which many people lose sight of. Some vets are ethical and don’t push expensive tests. Others … not so much. Vets can make money by suggesting further testing, special diets that they sell, treatment … there is a definite conflict of interest that can exploit loving pet owners’ worst fears.

So, if you’re curious about whether your pup has some Puli or Xoloitzcuintli in his past (unlikely), go ahead and do the test. Just don’t base decisions about his medical care on the results. Train, and care for, the dog in front of you — his behaviors, his quirks, and his medical symptoms.