Today’s article is inspired by one of our readers who purchased a Collie x Whippet puppy from a breeder. Anyone familiar with Whippets knows that they are one of the longest-legged breeds of dog out there… and Collies aren’t that much different! Yet 6 months down the line, the owner has been surprised to find their pup’s legs still short and stubbornly refusing to grow… 

So what’s going on? Is this Whippet-cross not entirely what they expected? DNA testing can be used to identify the different breeds mixed in with a dog. And might have been used to determine exactly what made up this exciting new short-legged “breed”. However, it’s not an exact science. So for today’s article, we are discussing dog DNA testing and if it is reliable.

What is DNA Testing? 

If you remember back to your upper school biology classes, you will remember that DNA, or deoxyribonucleic acid, is the backbone of our genes. Genes define almost everything about us, from our sex, hair colour and height; to our production of cells, enzymes and protein, and even our likes, dislikes, personality and how we think! Pretty much everything that makes you ‘you’ is initially determined by combinations of genes being switched on or off. Of course, other factors, like where you were born, past experiences, diet and health, and even luck influence traits too; we are more than our DNA. 

DNA testing, or more accurately genetic testing, involves looking for changes, or mutations, in normal genes, chromosomes (groups of genes) or proteins made from genes. Each gene codes exactly for a specific function, so a mutation can result in dysfunction. Early genetic testing in the 50s and 60s only looked at large chromosome mutations, helping to diagnose disease like Down’s Syndrome. Nowadays, more advanced techniques looking at genes specifically can be used for a myriad of reasons in humans. Including diagnosing disease, identifying if a baby will have genetic deformities, determining a person’s risk of cancer or other diseases, working out the risk two people will have of producing a baby with certain conditions, identifying the best treatment for certain diseases, and many more. Genetic testing has revolutionised medical care and will only get more useful as the science advances. 

DNA Testing in Dogs

That’s all very interesting, but what is the relevance to dogs? Well pets can now have genetic testing as well!

Using only a sample of blood, a cheek swab or similar sample, we can use genetic testing for similar reasons as in humans. We can look for disease, or the likelihood of it. We can also assess the likelihood of puppies from two parents having certain diseases. The UK Kennel Club uses genetic testing for a great purpose, identifying the risk of puppies having disease based on the parents’ genetics. By only allowing dogs with low risks of producing disease to breed, they are trying to reduce the incidence of some rather nasty genetic diseases.

And, of course, we can use genetic testing to identify what sort of breeds might be mixed into one dog. Many private companies are offering this service online. It can be as simple as swabbing your dog’s cheek, sending it off in the post and waiting to find out your dog is part Huskie, part Doberman, part Shetland, part Staffie and part Chinese crested! Some of these companies are also offering similar disease-risk testing to the Kennel Club and veterinary practices. 

Is DNA Testing Reliable?

We all know that no answer to any test is 100% reliable – just ask all the lateral flow tests! But how does genetic testing stack up?


Firstly, we should look at accuracy. This measures if the results produced are correct or not. If a very accurate test comes back positive, we can be more certain the true answer is positive. If an inaccurate test comes back positive, we are less certain the true answer actually is positive. 

Genetic testing accuracy is affected by a huge variety of factors. Including the sample submitted, the method of testing and the testor’s skill or lack of errors. With online testing, it can be hard to assess the accuracy of their tests. Many of these companies are not fully regulated. In fact, the American Kennel Club even says that because many companies keep their testing methods secret, it can be difficult to know how accurate results truly are. In short, take each result with a pinch of salt – it may well be inaccurate. 

Interpretation of the results

The second factor to assess is the actual interpretation of the results. If we assume the results are 100% accurate, is a dog carrying a gene for sudden blindness guaranteed to go blind? And if a dog lacks a gene for heart disease, is it guaranteed to never get heart disease? The answer for both of these questions is most definitely ‘no’, for multiple reasons.

To start, carrying a mutated gene is no guarantee the gene will be working. Many genes remain inactive or require other genes to function. Furthermore, many diseases are coded for by multiple genes.

Our genome (all our genes) is huge and impossible to assess all at once. So we tend to just look in specific places for key genes. By doing this, it can be easy to miss other genes that may make having certain conditions more or less likely. And remember that genes are also influenced by environment and other factors. A dog with a gene making heart disease more likely may never get it unless it is eating certain foods or doing certain things. Dogs have been sadly put to sleep just on the off-chance they may get a disease in future. And it goes the other way too. Companies reporting a dog cannot get a disease based on the lack of one gene can give people false hope. 

One geneticist summarised dog genetic testing nicely by saying, “the one question that you as a pet owner ask is, “What is the chance that my dog is going to get sick?”.” The geneticist said, “that’s not a question that we can actually answer yet.”

So What Happened with the Short-legged Whippet?

Moving away from disease testing and back to breed testing. If we assume the breeder was honest and tested the puppy using an online DNA test that reported the puppy was in fact the cross they said, this clearly demonstrates how genetic testing for breeds can be wrong, for all the same reasons listed above. This is likely how a “simple” cross turned out something different! The hypothetical genetic test performed did not identify genes from any other dogs so reported the dog was a mixture of those two breeds only. Genes from other breeds were either not identified properly or not even spotted. This is sadly really commonly reported. Especially with crossbred dogs where there are a number of different sets of genetic sequences interacting.

The alternative solution links to terminology. If you have read our article on ‘are cockapoos a real breed’, you will remember the issue with the term ‘purebred’. A purebred dog must be bred from the same two breeds. But because the parents are not always of proven lineage, there could easily be some other breed mixed in there. Pedigree dogs registered with the UK Kennel Club do have proven lineage, so you can be certain a purebred pedigree dog has only that breed in its DNA (at least as far back as the late Victorian era… see the cockapoo article for more details.).

Even if the breeder was certain the parents of the pup were both ‘purebred’, if they weren’t ‘pedigree’, there is no evidence to prove other breeds didn’t get their genes into the genetic soup in the last 150 years. Again, DNA testing may have shown a mix of other breeds, or may not have.

In this case, sadly, there’s a third explanation: that the father isn’t actually the father. And if the father was, say, a Collie-Daschund cross, he might well have passed on those short-legged genes along with enough Collie genes to fool the test!

What is the Moral of this Story?

Today we’ve used the story of the short-legged Whippet cross to deliver an important message. Any test, whatever is being tested for, is never 100% reliable. This includes tests performed by a vet (though they tend to be more reliable).

Genetic testing is a wonderful powerful tool. Whether you are using it just to find out what is mixed into your dog, guide breeding or identify potentially harmful diseases, always take the results with a pinch of salt. Breeding is perhaps the one area where having a chance of a disease is enough evidence to not breed – but treating an animal for a medical issue based solely on a genetic test is not good practice. We as vets can use the information you receive from them though – genetic tests can identify potential risks so we can give you advice on early warning signs for the specific diseases, as well as help us perform further testing for the diseases if needed.

In future, genetic testing is likely to get even more reliable, and who knows what we might be able to test dogs for in future – but for now, genetics is a science we have yet to master.

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