Ask Surly Amy and Elizabeth: Cats, Genetics and Diseases
Message: Hi guys. I need your help to clarify a question that’s been bugging me for a while now. I’m a crazy cat lady and so is a friend of mine. We meet over coffee to discuss our “babies.” She said her cat – a beautiful Norwegian with probably the lushest coat I ever saw on a cat – was falling ill (urinary tract problems mainly) because it was not a pure breed but had some Maine Coon blood. Now, if I understand things correctly, that should not be the case – introducing new genes in a gene pool, diversifies it and leads to healthier specimens because it makes genetic abnormalities less likely to occur. I have two ferals at home who NEVER fall ill, eat trash (not that I feed them trash, but they find their way to raid trash cans), drink toilet water and nothing touches them. The Norsk skogkatt is a natural breed, so I thought that like the feral it would have a higher chance of a wide gene pool or at least would be healthier than the man-made, inbred breeds.
This question wasn’t originally sent in as an, Ask Surly Amy. It was just a was a general question sent in by a reader to our contact form, but I snagged it! Because I knew I had the perfect person to help answer it!
That perfect person is one of the contributors over on Mad Art Lab, the super-smart and talented, Elizabeth Finn. Elizabeth is not only a creative-contributor to Mad Art Lab, she is also a Doctoral Candidate in genetics at Stanford University. She is our go-to gal for all our super-geeky genetics questions over at the lab and she was more than happy to give us a quick, yet detailed response, as to why mixed breeds aren’t always free from diseases.
Hybrid vigour is a real thing, and probably what the letter-writer is referring to. If you take two very inbred animals, and cross them, the resulting animals will generally be healthier than either parent. And this is for essentially the reason she describes: most genetic disorders are recessive, and so more heterozygosity in a genome, which is created by crossing two different inbred lines, means fewer genetic disorders. But there are some caveats here, particularly:
As you start breeding back onto either of the parental inbred lines, all of the disorders come back. Assuming there /is/ a disorder, and that the hybrid escapes it by being heterozygous, then crossing back to a parental line will uncover that disorder 1/2 of the time by the first generation, 3/4 of the time by the second generation, and 7/8 of the time by the third generation. Genetic diversity via hybridization disappears very shortly after that hybridization disappears. So knowing a cat is “part” Maine Coon doesn’t really help.
This also assumes that the disorder is (1) genetic and (2) recessive. I am not a veterinarian, but WebMD suggests many issues that could cause these issues other than congenital problems. So it very well might not be genetic. And while many genetic disorders are recessive, the most common genetic disorder in cats (feline hypertrophic cardiomyopathy) is dominant, and as such wouldn’t be subject to changes based on hybrid vigor or heterozygosity.
Hope that helps!
And to our reader, urinary tract infections often have dietary causes and nothing to do with genetics so that may be something for your friend to bring up when next speaking with her vet.
Now, go snuggle those kitties while you can and happy holidays from all of us at Mad Art Lab and at Skepchick!
Got a question you would like some Surly-Skepchick advice on? Send it in! We won’t publish your real name, unless you want us to and creative pseudonyms get bonus points! Just use the contact link on the top left of the page.
Surly Amy art by Jill. Photo of Rebecca’s cat by Rebecca.