Genetic Tests...Are Mixes Healthier than Purebreds?

It would certainly seem so...every day you hear about how this breed or that breed has some health problem or another. But how can this be? As a breeder I’d like to clarify…the problems didn’t come from the “purebred" in the dog - but were there all along because it’s a DOG. All dog breeds are 99+% the same genetically - and even toys and unusual breeds are 99+% genetically the same as the wolf they are descended from (that’s why they can interbreed). Of course, there are no statics kept on the various mixes and remixes out there...one reason you never hear about the Poodle x Shepherd x Daschund's problems.

Genetic diseases appear because the genes causing the disease are "expressed" - or allowed to do their dirty deeds. Often you’ll find mixes SEEM to be healthier than purebreds and the reason is because of what’s called “hybrid vigor". In other words, there are special genes that mask or stop other genes from working, so they aren’t expressed. It’s not that the disease genes aren’t there, they are just hidden. Purebreds eliminate a few of these genes so that what you see is what you get – whereas mixes often have the same problems, but  no selection has taken place so the "hiding" genes are still in place -   you may never “see" the disease – but it’s there under the surface. Often it will show up in a 2nd generation (called the F1 generation) when two mixes are bred together. They aren’t getting problems from the purebred - a mix that shows up with a disease just happens to be lacking the gene that hides the problem under the surface. In purebreds, the genes that hide other genes often are elminated due to selecting for certain traits as they appear, and are removed along with the health problems they mask, by selective breeding. 

Just wanted to clarify because there is this perception that mixes don’t get diseases or that purebreds are somehow inferior healthwise – no, they are all the same…it’s the fact that in mixes the problems are hidden behind ‘cloaking’ genes, and not out in the open. A Klingon is still a Klingon even if he’s behind his cloakng device.

The only way to be certain your dog doesn't have the gene for a particular genetic disease is to do a DNA test.  These tests can be done on most mixes as well, but rarely are.  DNA can only tell you if the gene is present - not whether it's masked or hidden.  So since mixes are seldom tested, and the cloaking gene isn't tested for, then of course the Purebred will appear to have more genetic disease. 

The advantage of a purebred dog is that they are DNA tested so you know for sure what's hiding under the cloak.  And reputable breeders will remove dogs with defective genes (and as a side, their cloaker genes) from the breeding pool.However, life is not perfect...sometimes when you try and eliminate the bad gene, all you remove is the cloaking gene.  Sometimes you only remove the bad gene (and the cloaking gene stays put)...but nobody cares when this happens.  With a mix there isn't this removal of one or another type of gene....the cloaking genes continue to live on hiding defects until they reappear in the next generation.  With a purebred, there is the actual elimination of the defect when it appears (assuming you have a responsible breeder who is trying to eliminate it), it's not just hidden for someone else to deal with. 

Contact Laboratory Sources:

1.Alfort School of Veterinary Medicine, France: https://www.labradorcnm.com/
2.Animal Health Trust (England): https://www.aht.org.uk/sci_diag_disc_genetics_dna.html#canine
3.Auburn Univ.--Boudreaux Lab: (334-844-2692)
4.Cornell--Goldstein Lab: (607-253-4480)
5.Cornell Univ. Comparative Coagulation Lab: https://www.diaglab.vet.cornell.edu/coag/test/hemopwh.asp (607-275-0622)
6.GenMARK: https://www.genmarkag.com/home_companion.php (877-766-3446)
7.HealthGene: www.healthgene.com (877-371-1551)
8.Jefferson Medical College: David.wenger@mail.tju.edu (215-955-1666)
9.Michigan State University-Malamuteerson-Jones Lab.: https://www.cardigancorgis.com/ (517-353-3278)
10.Michigan State University-Fyfe Lab.: https://mmg.msu.edu/faculty/fyfe.htm (517-355-6463x1559)
11. Washington State U--Pharm Lab: (509-335-3745)
12.Optigen: www.optigen.com (607-257-0301)
13.PennGen: www.vet.upenn (215-898-8894)
14.UC-Davis--Lyons Lab.: https://www.vgl.ucdavis.edu/service/cat/PKD.html (530-752-2211)
15.U Missouri--Johnson Lab: https://www.caninegeneticdiseases.net/ (573)-884-3712)
16.Univ. New South Wales--Wilton Lab: a.wilton@unsw.edu.au
17.List of Canine and Feline genetic tests
18.VetGen: www.vetgen.com (800-483-8436)
19.Washington State U--Meurs Lab: (509-335-6038)

From the AMCA Newsletter 12/2009

DNA Genetic Testing for various Breeds

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