The modern dog exhibits an extremely wide range of body types and behaviors. This is a particularly surprising fact in the sense that all dogs descended or branched out from the gray wolf some 15,000 years ago. The variety seen in the modern dog is solely due to selective breeding by man.
Researchers at the National Human Genome Research Institute (NHGRI) have been studying the genetic basis of several traits, in particular size variation, comparing the DNA of Chihuahuas, toy fox terriers and Pomeranians with large dog breeds such as Irish Wolf Hounds. Saint Bernards and Great Danes. (Source: Scientific Blogging, April 5, 2007)
Their research found that one gene is strongly associated with small sizes in all of the dog breeds studied; this same gene is present in humans and is probably associated with short stature in humans. These scientists are studying dog traits and gene mapping to gain a better understanding of how genetics cause particular traits in humans. Why study genetic traits in dogs?
The answer is selective breeding by man that restricted the amount of variation within the gene pool. There is less variation in the dog population than in humans, particularly for purebred dogs. There are just over 200 breeds of dog – the American Kennel Club recognizes over 160 breeds and has set standards for those breeds.
Genetic variation can be related to a simple example of probability. I have a bag of black and white marbles; There are 50 black marbles and 50 white marbles in the bag for a total of 100 marbles. The probability of catching a black marble is 50% (50/100). If I add 100 more white marbles to the bag, the probability of removing a black marble from the bag is now 25% (50/200). If I add more than 30 different colors of marbles and increase the number of marbles in the bag; the probability of catching a black marble will decrease significantly. The group of purebred dogs would equal the bag of 100 black and white marbles. Humans would be the largest bag with many colored marbles.
Gregor Mendel’s work with pea plants laid the foundation for our modern understanding of how traits are passed down from one generation to the next. What is learned from dog genetics and trait transfer regarding body structure, behavior, and disease may be directly related to human health and biology. Researchers can focus their research on the genetic causes of cancer and other diseases.