DNA testing has been around for a while, and unfortunately it earned a bad reputation when the OJ Simpson prosecutors miffed their explanation of it to the innumerate jurors on the case. And indeed, in the 1990s, DNA testing was an arduous and complicated process.

I know this from personal experience. I spent a summer (it was winter there) in 1998 in southern Chile running DNA tests on samples of salmon, looking for DNA of a parasite called Nucleospora salmonis. I spent my time toiling in the laboratory running the arduous, time-consuming, and error-prone polymerase chain reaction (PCR — which is how all DNA tests are run) with the beautiful fjords of the country just a stone’s throw away. I would have greatly preferred to be exploring those fjords.

That was then. It turns out that PCR and DNA testing have made technological advances that basically follow Moore’s law. What used to be an error-prone, multi-day process now has boiled down to dumping a sample into a machine. The only real errors made in current DNA tests occur when samples are mislabeled by people involved in the testing.

DNA testing has become so easy and cheap that in 2007 it spread as a curiosity to the world of dogs. That’s when Mars Veterinary (yes, that Mars, the one that makes Snickers bars) launched the Wisdom Panel doggie DNA test.

The purpose of the Wisdom Panel, and several other dog DNA test kits that have since launched and folded, is to identify the breeds in a dog.

Identifying the dog breeds that make up a mutt is an armchair hobby for most dog lovers and almost all veterinarians. Dogs in shelters generally get labeled based upon their appearance and behavior. For instance, my pal Buster was listed as a black Labrador Retriever mix. His appearance, along with his penchants for fetch, swimming, food, and love are all 100-percent consistent with that. But is he truly descended from a line of Labrador Retrievers?

Who cares? It’s irrelevant. He is what he is.

But wait, you say. Labrador Retrievers have certain disease predispositions. They have breed predilections to hip dysplasia, pericardial effusion, and megaesophagus. Wouldn’t knowing his true lineage be of medical utility?

The answer, simply, is no.

Dog DNA tests have been marketed — carefully, without too much commitment — as useful for predicting breed predispositions. But in reality they are nothing more than tools to satisfy, and in many cases stimulate, curiosity.

Dog DNA tests are proprietary products, so I am not privy to their exact details. But DNA testing in general works by studying certain “signatures” in the genetic codes. The people designing dog DNA tests undoubtedly have studied the DNA of various breeds and found signatures consistent with those breeds in their codes.

But those signatures have nothing to do with the essences of the breeds. They’re not the signatures that identify the genes for black hair, strong appetite, love of fetch, and friendliness that characterize a typical Black Lab. And, crucially, they’re not signatures that identify a propensity for hip dysplasia, pericardial effusion, and megaesophagus.

The signatures, essentially, are random. They are correlated with breeds, but they are not the essences of the breeds.

And those random signatures, which have statistical correlations with certain breeds, can lead to a bunch on nonsense when DNA tests are run on mutts. The stories of quirky DNA test results are legion.

I know a colleague who owns a large hospital. He was offered a free DNA test for his 100-pound dog by the manufacturer’s representative (who hoped, in turn, that the hospital would pimp the test to its clients). Everyone laughed at the results, which came back something like an even mix of Yorkshire Terrier, Chihuahua, Teacup Poodle, and French Bulldog.

Several of my coworkers have experienced similar results. A 30-pound terrier at my office came back as 75-percent American Staffordshire Terrier and 25-percent French Bulldog (apparently the Frenchie signature really shows up a lot). A recent client’s 125-pound dog that looked like a mix of Mastiff and Shar-Pei tested as 50-percent Boston Terrier, along with a hodgepodge of other breeds, none of which were Shar-Pei.

That last case is relevant. The dog had a fever and swollen joints. I was worried about the potential for familial Shar-Pei fever. Did the dog’s DNA test mean that I could rule out the syndrome?

No. It meant nothing.

Doggie DNA tests are interesting, but they are medically irrelevant in my opinion. A dog that tests as 25-percent Labrador Retriever and 75-percent Boston Terrier is not the descendant of a Boston Terrier who hooked up with a dog who, in turn, was the result of a tryst between a Boston Terrier and a Labrador Retriever. Such purebred dogs simply are not running around loose and knocking boots with each other.

A dog that tests as 25-percent Labrador Retriever and 75-percent Boston Terrier is a mutt with random DNA signatures compatible with Labs and Bostons. But he’s a mutt above all else. And I use the word mutt with pride. My dog is a mutt, and I am a mutt. Heck, even the President of the United States takes pride in being a mutt.

So, DNA-based breed testing is fun and interesting, but at the current time it serves little purpose other than entertainment. But that does not mean that DNA testing has no place in veterinary medicine. Although my pal Buster’s breed heritage is irrelevant to his life and mine, his specific genetic predispositions are highly relevant.

Genetic tests for specific medical predispositions, like 23andMe, have not yet entered the mainstream of veterinary medicine. But such tests are becoming more widely available through reference laboratories, and cheap, do-it-yourself versions inevitably will become available to the general public.

Such tests, unlike DNA-based breed tests, will no doubt dramatically impact the future not only of veterinary medicine, but also of dog breeding.

Learn more about dogs with Dogster:

• The 10 Biggest Misconceptions About Guide Dogs for the Blind
• 6 Things to Remember When You Have a Fearful Dog
• Four Things You Should Know About Your Dog’s Growl

Got a question for Dr. Barchas? Ask our vet in the comments below and you might be featured in an upcoming column. (Note that if you have an emergency situation, please see your own vet immediately!)