What Kind of Dog Is He? DNA Can Tell Me Only So Much.

NASHVILLE — Rascal is a small dog, not quite 13 pounds, longer than he is tall. His feet point in one direction, his knees point in another, and his fur is equally mismatched: short and curly in places, long and curly in other places, and just plain long or just plain short in still others.

When animal control picked him up last spring, Rascal was fully grown, unneutered, and so tragically flea-infested that the shelter staff had to shave him. Well, they shaved him everywhere except his tail, which is covered by plumes of wiry hair bearing little resemblance to the rest of him. His fur may still be growing out, or it may be exactly as long as it will ever be. We don’t know yet.

The great parlor game of the mutt-dog world is Guess the Breeds in the Mixed Breed. Here is how the conversation always goes whenever Rascal and I meet someone new:

New person: “What kind of dog is he?”

Me: “I don’t know.”

New person: “Maybe some sort of [fill in the blank]?”

Reasonable guesses include Jack Russell terrier, wire-haired terrier, Yorkshire terrier, dachshund (or “Datsun,” as one person put it), and corgi, but he doesn’t look much like any of them. The paperwork from animal control calls him a Chihuahua mix. The paperwork from the rescue organization calls him a terrier mix. Our veterinarian declined to guess. “One hundred percent Rascal,” he said, laughing.

Mongrels are mysteries. They invite pondering in a way that purebred dogs don’t, never mind that two dogs of the same breed can also be very different from one another. People don’t stand around and guess at what kind of dog a pedigreed puppy will turn out to be. They think they already know.

My dog’s breed doesn’t matter to me, so I’ve always regarded DNA testing to be unnecessary. I wonder, too, about how reliable the results would be. Though the companies are continually updating the tests — screening for more breeds and more mutations, using more genetic markers — no government agency or peer review system independently verifies their accuracy.

More to the point, how would knowing Rascal’s breed mix help me understand this unique little weirdo we’ve adopted? Would it tell me why he’s terrified of even the tiniest puppy but thinks he can catch the UPS truck? Or why he prefers to sit on the highest point he can reach in any room? Why he ignores any normal ball but loves to play fetch with a dryer ball stuffed into an old sock? Knowing the breeds in his lineage might explain his allergies, but would it explain why he licks me incessantly whenever his ears itch?

Nevertheless, my curiosity is always piqued by other dogs’ DNA test results, some of which have been astonishing. Our son and daughter-in-law’s gentle black rescue dog, “a Border collie mix,” according to the rescue organization they adopted her from, turns out to be zero percent Border collie but 10 percent wolf. Only a tiny part wolf, but still. Not at the top of anybody’s guess list.

Curiosity is a great motivator, but my curiosity about Rascal’s breed mix would have come to nothing had I not submitted to a DNA test myself shortly before we adopted him. I wasn’t looking for my own genetic ancestry; I’m wary of what such tests reveal and warier still of how their results might be used. Commercial DNA testing has revealed family secrets, solved crimes long consigned to the cold-case files, even affected census results.

From human genetics research — particularly studies involving identical twins — we know that DNA influences much of what we consider to be our most human traits: our personality, our preferences, our I.Q. Lay people, even many researchers themselves, tend to find such research troubling, hinting at a kind of genetic determination.

Despite the unresolved ethical and cultural issues raised by DNA testing, its potential medical benefits are remarkable. I have a rare inherited syndrome that almost certainly killed my paternal grandmother at 51 and accounted for my father’s cancer diagnosis in middle age. When I submitted a saliva sample to a medical lab for genetic testing, I was contributing to research that might identify the gene that causes the condition, saving future patients from the expensive and disruptive cancer screenings that I undergo every year.

All of which primed me to reconsider DNA testing when we adopted Rascal; canine DNA tests can also reveal certain inherited medical conditions. In January, our rescue dog Millie died of complications of epilepsy. If Rascal carries a genetic risk for something terrible but treatable, too, I wanted to know about it.

Following a recommendation from Wirecutter, which evaluated 17 DNA tests on the commercial market, I ordered one from Embark and sent in a sample of Rascal’s saliva. A couple of weeks later, I got his results: 35.9 percent Chihuahua, 34.4 percent poodle, 6.9 percent bichon frisé and 22.8 percent supermutt, Embark’s catchall term for trace amounts of DNA from distant ancestors. Rascal’s ancestors apparently include a collie, a Pekingese, a Shih Tzu and a Maltese terrier.

The test also revealed that Rascal carries two copies of a gene variant associated with disk disease. Even before the breed results arrived, I got an email from one of Embark’s veterinary geneticists explaining the risks associated with this variant and recommending some mitigation strategies. Some of them, like using a harness on walks, were easy to do. Others, like discouraging jumping, were less so. Keeping this buoyant little dog earthbound is a fool’s errand, but I was extremely grateful for the detailed advice.

Breed mix remains a matter of indifference to me. What does it mean that my gentle granddog has a wolf somewhere deep within her lineage? Apparently nothing. That’s the mystery of individuality, even in dogs.

In nearly every creature, actually. Science is already providing evidence for what any pet owner, as well as any observer of the natural world, understands instinctively: that Homo sapiens is far from the only species in which individuals display unique personality traits. A great many creatures are as different from other members of their own kind as we are from one another, and it doesn’t fundamentally matter whether those differences are caused by DNA, or experience, or something ineffable that we have no name for yet.

As for Rascal, whose relationship with gravity is entirely provisional, perhaps he will slow down a bit as he ages, or perhaps he will continue to leap from chair backs to high beds to ironing boards. Still, and always, 100 percent Rascal.

Margaret Renkl, a contributing Opinion writer, is the author of the books “Graceland, at Last: Notes on Hope and Heartache From the American South” and “Late Migrations: A Natural History of Love and Loss.”

The Times is committed to publishing a diversity of letters to the editor. We’d like to hear what you think about this or any of our articles. Here are some tips. And here’s our email: [email protected].

Follow The New York Times Opinion section on Facebook, Twitter (@NYTopinion) and Instagram.