In Dog Genome, Scientists See Man's Best Hope

By David Brown
Washington Post Staff Writer
Thursday, December 8, 2005

There probably isn't a tail-wagging gene or a face-licking gene. But there undoubtedly are groups of genes that explain why retrievers chase sticks, spaniels jump in the water at every opportunity, and border collies like to herd sheep and small children.

The biological basis of the astonishing variety of behaviors of man's best friend is a big step closer to comprehension today with the publication of the dog's genome -- its 2.41 billion nucleotides, or DNA "letters."

The dog -- in the form of a female boxer named Tasha -- joins the human, the chimpanzee, the mouse and the rat on the list of mammals whose genetic instruction manual has been transcribed. The genomes of the fruit fly, a microscopic worm, yeast and several bacteria have also been decoded.

But the dog genome is far more than a curiosity. It is already providing insights into evolution and will probably make dogs the chief tool for understanding the genetic diseases of people.

Certain breeds are at much higher risk than others for specific ailments. Samoyeds have a tendency to become diabetic, Rottweilers develop the bone cancer osteosarcoma, springer spaniels are at risk for epilepsy, and Doberman pinschers suffer from narcolepsy much more often than other canines. All these diseases have human counterparts.

"This offers a strategy for tracking down the location of genes involved in medical conditions that in the past we have just not been able to tackle," said Francis S. Collins, director of the National Human Genome Research Institute, which helped pay for the work.

Eric S. Lander, director of the Broad Institute in Cambridge, Mass., where the research was done, said: "The genetic structure of dog breeds is so much clearer than in the human population that it will make genetic analysis much simpler."

The work is the product of nearly 250 scientists organized through the institute, which is affiliated with Harvard and the Massachusetts Institute of Technology. A much less detailed version of the dog genome by a different research group was published two years ago.

In size, appearance and behavior, the dog is the most diverse species on Earth. It was the first animal domesticated from the wild, at least 15,000 years ago. Its many subspecies, or breeds, were sculpted by man, so it's no surprise that man should want to shine the illuminating light of genome science on his longtime companion.

A genome is the total mass of genetic instruction an organism inherits. It consists of strings of DNA nucleotides, the biological equivalent of letters. The instructions on how to build a body -- including permanent structures such as teeth and brain cells as well as short-lived substances such as blood and hormones -- are contained in the order of the nucleotide "letters" on the strings. Humans have about 3 billion nucleotides in their genome.

Stretches of hundreds or thousands of nucleotides are copied inside cells and direct them to produce specific proteins, the building blocks of organisms. These stretches are called genes.

Humans have about 22,000 genes. Dogs, according to the new research, have about 19,300. A given gene usually comes in slightly different variations, similar to pencils with different colored lead, or scissors of varying size and shape.

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