brookcove
Posted : 7/26/2009 4:16:20 PM
but that the breed "needs" hairy-hairless is questionable
This goes back to the working question. The problem is that when we narrow down the gene pool for arbitrary reasons (like aesthetics and fancy versus health, temperament, and structure), we have no idea what we are cutting out, due to the connectedness of genes.
The Border Collie and the Rough/Smooth Collie were once the same breed. The division into working/show occured in the 1870s. Today, the genetics for "normal" eyes versus CEA is very low in the show collie, possibly as low as 15%. In Border Collies (the "working" branch), 93% of the breed is normal, or unaffected.
Certainly the show collie breeders cared about the health of their dogs. In fact, these lines are more "carefully" bred than the farm dogs, who basically went by the "survival of the fittest" rule and were largely random bred in all regards except function.
So when did the phenotype for abnormal eyes begin to creep in, higher and higher? No one knows, of course. There still is not a good way to tell what alleles are linked together, other than guessing based on experience.
Even more striking is the MDR1delta mutation which occured almost immediately after the show breed branched off. In spite of the 100% shared gene pool at the time (circa 1870), the genetic test available today has shown that the incidence of the mutation in Collies is around 33%. It is ZERO percent in Border Collies.
Today in the Border Collie, there is a discussion going on concerning inbreeding coefficients and their influence on the health of the breed. The BC has a very healthy overall COI, probably around 7%, but there's some concern that "pedigree breeding" is replacing careful attention to working style and the needs of the individual stock operation. This leads to concentration of "founder dogs" and unwanted traits they carry, rather than maintaining balance and continual outcrossing back and forth across lines.