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A blog by Jane Brackman, Ph.D.
jlbrac@earthlink.net

Monday, February 17, 2014

Are Pedigreed Dogs Unhealthy?

The answer is some are. And this is one reason:

I came up with this analogy to explain how the canine genome has been compromised as a result of modern breeding practices. I think about this stuff a lot because I write about canine genetics and I'm always looking for ways to simplify complex topics.
The fragile purebred canine genome

Like pulled-thread needlework, where the pattern is created by removing threads from the warp and weft of a piece of even weave fabric, traits that define purebred dogs are created by removing genetic variations that breeders find undesirable.
Think of this as the generic dog genome
 All traits are here, some hiding and some expressed.
Traits removed by breeders might be anything from kill-instinct to black spots on a white coat. Some genes are completely wiped away and cannot be reclaimed within the breed.

Rigorous selection is the pulled thread that defines purebred dogs.  
Beautiful? Yes.


But the integrity of the fabric can be undermined and weakened as a result. In purebred dogs, a few genes may control multiple traits. Pull one thread and out comes another, perhaps unintentionally.   For instance, in the Dalmatian, when breeders selected for coats with fewer spots, they were eliminating the genetic variants that not only control pigment, but are also responsible for building parts of the ear.  As a result, they inadvertently created a population of deaf Dals.
In Dalmatians, removing spots may also remove genetic variants responsible for ear development.


Although it doesn't fit with my pulled-thread analogy, adding or emphasizing traits can magnify unwanted genetic variants that might be related to diseases.

Too much of a "good" thing?  Scientists have identified a relationship
between skin wrinkling and Shar Pei Fever


And finally, the genome is not static. Fragile purebred genomes can be further undermined by random mutations. Genetically diverse breeds don't suffer as much, because they are better able to compensate.

The good news is that dogs with genetic issues can be out bred to similar breeds.  The genetic variants that cause the flaws are not eliminated, but they are diluted, meaning the chance of showing up as traits is significantly reduced. For instance, Dalmatians bred to Pointers for several generations and then bred back to Dals are much healthier than their purebred counterparts. But like everything else with purebred dogs, it's controversial.
Dalmatian-Pointer back crossing reintroduces healthy genes, eliminating many painful diseases that Dals suffer from.

2 comments:

  1. Dalmations with fewer spots?! I thought spots were the whole (or at least major) point of dalmations. I like the comparison to needlework.

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  2. Very interesting! and I like the analogy too, easier to understand the process. It doesn't sit easy with me, all that refined selective breeding stuff, much prefer to let dogs be who and what they are.......Dalmations look great just the way they are.......

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