SHIH TZU FANCIERS OF SOUTHERN CA

THE AA BB CC'S OF DNA

Careful selection by mankind throughout the centuries has resulted in genetic diversity within dogs that is unprecedented in any other mammalian species. Although there is still a long way to go before scientists fully understand the complexities of the canine genome, they are well underway. And as scientists come to know more about canine genetics, the results will likely be interesting, important and probably surprising.

Among the many advances in genetics in recent years is the ability to sue certain genetic markers in a dog's DNA for the production of a unique genotype. The method provides absolute identification of individual dogs and parentage verification from one generation to the next. (It does not provide instantaneous identification and therefore does not replace other methods used during kennel inspections.)

All breeds have the same genes, as well as a finite number of gene pairs. Although there is some speculation about the exact number, it is estimated that dogs possess between 50,000 and 100,000 gene pairs in every cell. Variations of these gene pairs, called "alleles" exist for every gene pair. Alleles account for the difference between Chihuahuas and Saint Bernards, and all breeds in between..

A dog's genetic constitution called a "genotype," can be determined by a analysis of a simple bristle swab swirled against the inside cheek portion of a dog's mouth. For example, a possible analysis for a dog taking part in the AKC's Voluntary DNA Certification Program, which tests for 10 gene pairs, might read BD/CE/DD/DZ/EG/CC/GH/CD/CF/AA. Each letter represents one member of a pair of genes, and each gene pair is represented by two capital letters.

For example, "AA" means that on a specific chromosome pair, one chromosome has "A" at a specific site or "locus" and the other member of that pair has an identical "A" allele or gene. Dogs have 78 chromosomes (38 pairs + XX in females and 38 pairs +XY in males) and these are numbered 1 through 38, plus the X and Y chromosomes.

Why test only 10 gene pairs? Because each of the 39 chromosome pairs contains 50,000 to 100,000 gene pairs, it is impossible, prohibitively expensive and unnecessary to test thousands. It has been determined that testing 10 pairs distributed across the 39 chromosome pairs is mathematically sufficient to establish a unique identity.

Among different breeds are different gene frequencies, which means that specific alleles occur more or less frequently than others. One goal of the Parent Breed Club Program is to understand these using 17 markers and learn how to efficiently structure tests for parentage across different breeds. These results will permit the AKC to establish a program based on extensive knowledge of the genetic markers used across all breeds. No one has ever collected and analyzed this amount and kind of genetic variation in purebred dogs. The results will undoubtedly provide useful information to the fancy and to the scientific community.

How does this relate to parentage verifications? In every generation, there is a "shuffling" of genetic information. This shuffling is called "genetic recombination," and its consequences for breeders are extraordinary. For example, 50 percent of a dog's genes come from its sire and 50 percent from its dam, which means that 50 percent of a sire or dam's genes are not present in their offspring. It's no wonder that breeding great dogs takes understanding, dedication and patience. 50 percent of what you hope to see from any great sire or any great dam is discarded every time a new pup is born.

The shuffling of genetic information is responsible for both the successes and the failures as new pups are whelped. Without genetic variation, no new combinations would result and the genetic challenge of producing better dogs--by carefully selecting and breeding the best to the best--in succeeding generations would not be a reality.

What does all this mean for breeders? It means that we can now begin traveling down a long road--a road that begins with the absolute identification of each dog by DNA. and continues with foolproof parentage verification. It follows that the AKC registry will have absolute integrity. That fact closes the doors to possible questions about the registry, and permits fanciers to focus on what the sport is really all about--breeding better dogs.

by Dr. James Edwards

Dr. Edwards  is the AKC Compliance Operations and DNA Educational Services Director.

For additional information on the AKC's DNA Certification Program, go to the AKC website: http://www.akc.org

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