Dog DNA Tests: Mixed Results

DNA tests that purport to identify the breeds in your mixed-breed dog are still a work in progress but the technology improves daily.
By Kathryn Socie-Dunning
On a gorgeous spring day in Montana, I was heading back from a romp in the mountains with my three dogs when we stepped out of the woods into a meadow, replete with song birds and a smattering of open range cows grazing peacefully. My trail companions quickly discovered, to their absolute delight, fresh, delicious cow pies.

It occurred to me, however, that I didn’t know the MDR1 (multi-drug resistance gene) status of the newest member of my three-dog crew, Hap. MDR1 is a genetic predisposition to adverse drug reactions to more than a dozen common veterinary drugs, and the gene is found predominantly in herding breeds. Hap looks to be mostly Border Collie with maybe, just maybe, a pinch of Australian Shepherd, so having this predisposition could put him in danger in this situation. Cows are often given ivermectin as an anti-parasitic agent, and the drug can be found shortly afterward in their droppings; eating these droppings can cause a fatal reaction in a dog with the MDR1 mutation. So, I put a moratorium on the afternoon’s pie sampling, much to the dismay of my crew, and off we strolled into the sunset.

When we got home and I began looking up information on MDR1 testing, I learned that many of the genetic tests for breed-typing now also include genetic health screens, including testing for the MDR1 mutation. I thought, why not solve the mystery of Hap’s breed-mix and get health information at the same time? It sounded like fun!      – KATHRYN SOCIE-DUNNING

How Do Dog DNA Tests Work?
While some of the early mixed-breed identification tests used a blood sample, all of the products on the market today extract DNA from cells swabbed by the dog’s owner from the inside of the dog’s cheek. The swab is sealed in a container provided by the company and mailed off to the company’s lab. There, technicians extract your dog’s DNA from the swab, and use computers to identify and compare specific bits of it to bits taken from dogs of known lineage.

The genome of a dog contains about 2.5 billion nucleotides (the building blocks of DNA); researchers focus on “only” about 200,000 of these individual genes – or rather, microsatellites or repeating sequences of DNA called single-nucleotide polymorphisms (SNPs, pronounced “snips”) that form signatures particular to various breeds.

Researchers must have enough SNPs from enough purebred representatives of each breed in order to have an adequate array of SNPs to which they can compare your dog’s SNPs. The larger the company’s database of samples from purebred dogs, the better. When a company fails utterly to suggest ancestors of candidate breeds that are remotely likely, it’s probable that it lacks enough breeds in its databanks to find good matches for your dog’s SNPs.

When Dog DNA Results Don’t Make Sense

The companies that offer this service have a few standard explanations for results that don’t seem to make sense.

None of the companies would admit that their reference databases are of an inadequate size to accurately identify the SNPs from your dog – but they might suggest that this could be true of their competitors.

All of the companies will be quick to explain that there are hundreds of thousands of genes that are responsible for a dog’s appearance, and that many breed combinations result in dogs who look very different than what you would expect from that mix of breeds.

Also, genes in mixed breeds do not always combine in the same ways within all litter-mates, so size and physical and behavioral characteristics in the same litter of pups can and often do vary, sometimes wildly. 

They also explain that the complexity of your dog’s mix will affect the accuracy of the results.

First-generation crosses between two purebred parents are relatively easy to identify, but dogs who don’t have any purebred ancestors within several generations are much harder to identify with much certainty, as the length of the inherited SNPs that are unique to purebred dogs become much shorter with each generation of mixed-breed progeny.

Problems with identification can also arise when there is a lot of divergence within a specific breed-type, like in the case of Australian Shepherds and Border Collies, where you have field-bred lines and show-bred lines. The genetic signatures in the companies’ databases usually correspond with show-bred lines, so field-bred Aussies and BCs might even get assigned to a different breed altogether.

Embark and Wisdom Panel make it easy for consumers to contact them and ask questions about their dogs’ results. I called and asked a representative from Wisdom Panel to review Hap’s results with me and was told that the statistical confidence in the Boston Terrier finding was marginal, meaning there is a high probability this result is not correct. Hap could have 12 percent of something not represented in the Wisdom Panel database (such as field-bred Australian Shepherds), but since this unique signature does not currently exist in the database, he was assigned to the breed with the closest matching genetic signature. I was told that updates will be made to Hap’s report as new information is added to the database.

Otto’s Results

Otto’s results have morphed over the past eight years, with the unlikely Basenji disappearing and a bully breed and Australian Cattle Dog appearing in the mix. Note that the results provided by the two leading mixed-breed test providers are pretty darn similar – and that the results from the smallest company offering this service border on fantasy. (Those breeds are highly uncommon in Otto’s area of origin, and would be even more uncommonly seen in the same dog.)