DNA Tests – Information or Entertainment?

July 19, 2017 - by Gemma Davis - in Uncategorised

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Dr Rowena Buxton

In parks around the world dog enthusiasts have developed a hobby that transcends geographical boundaries. Veterinarians, breeders and pet owners alike cheerfully participate in “Name that Breed”, a game becoming ever more popular as the adopted and rehomed pet slowly nudges the purebred off the couch. DNA testing, a technology now familiar to us from television shows and newspaper reports, has the potential to be a game changer for those enthusiasts, but how accurate is it? How much can a Dog Breed DNA Test really reveal about your pet?

The breed DNA tests have been around for about ten years now, and while the results have improved, the technology behind the tests is essentially unchanged. DNA tests rely on the identification of unique sequences in DNA codes. As more samples are submitted and tested it becomes possible to locate strands within DNA that are found always and only within members of certain breeds.

To design a Dog Breed DNA test it is only necessary to find a small section of DNA unique to that breed. Every time the unique sequence for Chihuahua’s is revealed in a DNA sample, it is possible to say that the individual in question has a Chihuahua forebearer.

But there is a catch. Having the DNA signature unique for a Chihuahua does not mean that the individual also carries the larger DNA sequences that code for a small body size, huge personality or disproportionately large eyes. Thus the very large, rust coloured dog with long legs that for all the world looks like a Vizsla may indeed return a signature for Chihuahua parentage. Confusing, but possible because the sequence of DNA carrying information for size, coat colour and behaviour is not the same as the tiny bit of DNA that acts as a marker for the Chihuahua breed.

So if we assume that the Dog Breed DNA Test does exactly what it is advertised to do – identify breed signatures – how useful is this to veterinarians, breeders and pet owners interested in the health, vitality and welfare of the individual dog? Will knowing that your noble Vizsla’esque hound bears the mark of Chihuahua forebearer’s allow you to predict your pets’ longevity or your veterinarian to better schedule dental checks?

In short, the answer is no. Just as the breed DNA signature carries too little information to ensure that all the traits associated with the breed are expressed in the individual, certainly too little to guarantee short legs and a soft coat in our Chihuahua bearing, Vizsla’esque looking friend, the signature is too short to code for a collapsing trachea or luxating patella.

The DNA markers for specific disease conditions are not the same as the DNA markers for specific breeds, and while Dog Breed DNA Tests excite curiosity, they do little to improve our ability to predict the future for our furry friends.

What we can predict is that genetic tests for pets will move rapidly beyond breed markers. The number of genetic tests for specific medical predispositions is increasing – based on the same ability to detect signatures in the DNA, this time associated with disease. In the future it is likely to be more common to screen for specific medical conditions than breed heritage, and the results are likely to be much more useful in the prediction and prevention of disease.

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Gemma Davis

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