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.
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.|
|diseases that Dals suffer from.|