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Scientists Discover Sequence of Canine DNA Key to Diversity in Dog Body Size
According to Guinness World Records, Gibson, a Great Dane, is the world's tallest dog, from floor to shoulder 42.2". He stands 7'2" on his hind legs. Gibson plays with his friend, Zoie, a 7.5" Chihuahua.
[Image © Deanne Fitzmaurice]
Scientists have discovered a sequence of canine DNA key to the great diversity in the body size of dogs, from Chihuahuas to Grant Danes, according to research in the 6 April issue of Science.
In their research, Nathan B. Sutter, a geneticist at the National Human Genome Research Institute, and colleagues found that all small dogs share a specific sequence of DNA that affects insulin-like growth factor 1 (IGF1), a gene that has been implicated in body size in other organisms including mice and humans.
Through their DNA analysis of more than 3,000 domesticated dogs, which exhibit the greatest diversity in body size of any terrestrial vertebrate, the authors found the size-regulating DNA sequence present in all small breeds and nearly absent in all large breeds.
"The [sequence] is common to all small breeds and nearly absent from giant breeds, suggesting [it] is a major contributor to body size in all small dogs," wrote Sutter.
The authors' initial research focused on Portuguese water dogs—a breed that has an unusually wide range of skeletal size—but eventually involved DNA analysis of more than 143 breeds.
While the genetic origin of dog size diversity is vague, the authors hypothesize that humans may have bred dogs to meet physical limitations of their surroundings.
Previous archaeological studies have found 15,000 year-old Great Dane-sized remains in Eastern Russia and 12,000 year-old small terrier-sized remains in the Middle East, suggesting that the diversity may have been caused by "early humans or as an adaptive trait for coexistence with humans in the more crowded confines of developing villages and cities."
Evelyn Brown and Benjamin Somers
5 April 2007