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Background and Justification:
The dog, long known as "man's best friend", is commonplace throughout the world. Not only is this true today but it has also been true throughout the history of
man. "In searching for cultures without dogs since prehistoric times, we came up empty-handed, with the earliest breeds coming from the Middle East, Africa and Asia (Thorpe-Vargus, Coile, et. al,
1998)". In other words, man and dog have shared this intimate friendship for a very long time.
These furry friends are descendents of the gray wolf, not the fox as earlier believed. Both dogs and wolves have 78 chromosomes while the fox has 36 chromosomes. Approximately 12,000 years ago man began
his relationship with the domesticated wolf and since that time man's manipulation of their breeding has given rise to all the fantastic dog shapes and sizes that populate our planet today (Mestel, 1994).
Dogs, cats, sheep, cattle, and horses are examples of animals that have been domesticated by man. Dogs were the first domesticated animals. Early man needed the canine's speed, power, skills, and
intelligence to help as he hunted. As man migrated throughout the world, their dogs migrated with them. As dogs demonstrated desirable traits or skills, they were bred to other dogs with similar traits
or skills (Zahorsky, 1997). This selective breeding led to the creation of different breeds of dogs. Some were capable hunters while others were valued for their ability to herd animals, pull cargo, or
guard their owners.
Currently, the American Kennel Club (AKC) recognizes 148 different breeds of dogs. A breed is defined as "a relatively homogeneous group of animals within a species, developed and maintained by man (AKC,
2000)." Of all of the mammals, dogs display the greatest genetic variety (McCaig, 1996).
Even though there is enormous variation among dogs they all belong to the same species, Canis familiaris. This determination is made because all dogs are able to interbreed and produce fertile offspring and
this satisfies the biological species concept (Mayr, 1982).
While dog is man's best friend, it remains to be seen if man is dog's best friend. While dogs have been selectively bred for desirable traits, breeders have also inadvertently selected genes for diseases and
disabilities such as hip dysplasia, blindness and deafness. A deeper study of the genetics of the dog will lead to better understanding, treatment, and eradication of these unfortunate abnormalities.
With biotechnological techniques available today, including polymerase chain reaction (PCR) and gel electrophoresis, not only can dog variations be studied at the morphological level, but they can be studied at the
gene (DNA) level as well. Following the lead of the human genome project, the canine genome project was established to map the approximately 100,000 genes of doggy DNA and their first chromosome map was
published in 1998 (Thorpe-Vargas and Cargill, 1998). The unraveling of this map will be instrumental in producing an evolutionary history of the breeds of dogs and understanding the many genetic diseases that
affect dogs. This hopefully will aid breeders in producing more healthy animals.
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