Domestic dogs exhibit the greatest range in body size of any mammal—from tiny Yorkshire terriers that fit inside a purse to gigantic Great Danes weighing upward of 200 pounds (90 kilograms).
But the genetic origin of this diversity has baffled scientists—until now.
Researchers have identified a variation in a single gene that plays a key role in making small dogs small.
"The best way to describe the role of the gene is, it's like the 'reduce' button on a Xerox machine," said lead researcher Elaine Ostrander of the National Human Genome Research Institute's Cancer Genetics Branch in Bethesda, Maryland.
More than 20 scientists from eight institutions in the United States and the U.K. participated in the study.
The findings appear in tomorrow's issue of the journal Science.
The discovery could ultimately lead to improved medical care for both dogs and humans, by helping scientists track down genetic causes for complex diseases such as cancer, diabetes, and hormone disorders.
Canines make good models for studying human health because they suffer from many of the same types of diseases and share the same environments, the researchers said.
Genetic Surprise
To conduct the study, the researchers traveled to dog shows and other events, collecting blood samples from 3,241 canines ranging in size from itsy-bitsy Chihuahuas to enormous mastiffs.
After analyzing the DNA, researchers discovered the genetic instructions for restricting growth were located near the gene named IGF-1, for insulin-like growth factor 1.
In humans and other mammals, the hormone regulated by IGF-1 helps animals grow from birth to adolescence. But in small dogs, the researchers found, one or more mutations located next to the IGF-1 gene did just the opposite and suppressed growth.
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