This short National Geographic piece explains how the enormous diversity of dog breeds can be explained away by a relatively small change in genetic manipulations:
The difference between the dachshund’s diminutive body and the Rottweiler’s massive one hangs on the sequence of a single gene. The disparity between the dachshund’s stumpy legs—known officially as disproportionate dwarfism, or chondrodysplasia—and a greyhound’s sleek ones is determined by another one.
The same holds true across every breed and almost every physical trait. In a project called CanMap, a collaboration among Cornell University, UCLA, and the National Institutes of Health, researchers gathered DNA from more than 900 dogs representing 80 breeds, as well as from wild canids such as gray wolves and coyotes. They found that body size, hair length, fur type, nose shape, ear positioning, coat color, and the other traits that together define a breed’s appearance are controlled by somewhere in the neighborhood of 50 genetic switches. The difference between floppy and erect ears is determined by a single gene region in canine chromosome 10, or CFA10. The wrinkled skin of a Chinese shar-pei traces to another region, called HAS2. The patch of ridged fur on Rhodesian ridgebacks? That’s from a change in CFA18. Flip a few switches, and your dachshund becomes a Doberman, at least in appearance. Flip again, and your Doberman is a Dalmatian.
This is in stark contrast to genes in humans, where something like human height is controlled by interaction of 200 or more genes. So why is there such a difference in dogs? The answer lies in domestication of dogs:
Sheltered from the survival-of-the-fittest wilderness, those semidomesticated dogs thrived even though they harbored deleterious genetic mutations—stumpy legs, for instance—that would have been weeded out in smaller wild populations.
The most fascinating part of the piece is the relevance of dog to human diseases, and how they may be related:
Cornell researchers studying the degenerative eye disease retinitis pigmentosa—shared by humans and dogs—found 20 different canine genes causing the disorder. But a different gene was the culprit in schnauzers than in poodles, giving researchers some specific leads for where to start looking in humans. Meanwhile a recent study of a rare type of epilepsy in dachshunds found what appears to be a unique genetic signature, which could shed new light on the disorder in us as well.
Here is the link to the Cornell genetic diversity project in dogs.
(hat tip: Andrew Sullivan)