The Nature of Genetic Defects -- Boerboel Breeders Info. Forum

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Date Posted: 09:13:10 04/17/04 Sat
Author: David I.
Subject: The Nature of Genetic Defects
In reply to: Jerry 's message, "The Man Who Bought A House" on 12:42:11 04/01/04 Thu

This bears some discussion. I hope others will let there opinions be known.

Full Article: http://www.seppalasleddogs.com/breeding3.htm#diversity
Auth J. Jeffrey Bragg
Exerpt
GENETIC DEFECTS -- WHY THEY EXIST: The dog breeding community is usually so caught up in reproaching one another over genetic defects, on the premise that if one's dogs have them it must obviously be due to "bad breeding," that it seems never to occur to anyone to ask why or how it can be that these things occur at all! Yet to ask this question, and to answer it, may give us the clue we need to deal with the problem.

Obviously most breeders have been selecting against genetic defects for a long time. Nobody intentionally breeds defective stock. Where did these genes come from, anyway? We're told that the domestic dog developed from the timber wolf, Canis lupus. The wolf has been an extremely successful predator species in the wild for tens of thousands of years, if not hundreds of thousands. Operating as he does in hostile environments and harsh climatic conditions, you'd think that the wolf would have had his genetic defects eliminated through natural selection a long time ago. And that's our clue.

If a gene, that in its homozygous form causes a defect affecting the animal's fitness for survival, is nevertheless retained for thousands of years, there has to be a reason. The gene cannot be neutral, even in its non-expressive heterozygous state; it would still be eliminated by natural selection over time. So it must confer an advantage in its heterozygous state. And this is exactly what evolutionary biologists and wildlife geneticists believe takes place. They call it overdominance or heterozygote superiority. What has to be happening is this: the so-called 'defect' genes are defective only when paired as homozygous recessives. When they are paired with another allele that is dominant, together the heterozygous gene pair confer a fitness advantage to the animal over either the dominant homozygous type or the recessive homozygote. That is the only possible way that these genes could be retained for thousands of years in a wild population.

So the veterinary professors and the breed clubs who prate about the "elimination" of various genetic defects are talking nonsense! They encourage us to engage in a fruitless struggle to eliminate something that nature herself has not seen fit to eliminate. It is not the gene that is at fault -- our breeding methods and our closed stud books are to blame! We have stripped away the natural canine dominant genes, leaving a residue of homozygous recessives that never should be expressed in the phenotype, because they should never occur in the homozygous state.

Doubtless all the various screening programmes provide secure employment for professors of veterinary medicine, lab technicians and foundation administrative staff. Yet should these peoples's vested interests take precedence over the health of our dogs?

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Replies:

Inbreeding and Diversity -- David I., 08:48:08 05/02/04 Sun
Re: The Nature of Genetic Defects -- Ed Davis, 15:51:03 05/15/04 Sat
- Inbreeding and Genetics -- David I., 19:41:01 05/17/04 Mon