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Sizing up man's best friend
Have you ever wondered why dogs come in such diverse sizes? When they are on their hind legs, the toy dogs may just reach up to your knee. The giant dogs can easily push you over and are more than 7 feet tall!
The domestic dog (Canis familaris) shows the greatest range of sizes of any mammal. Genetic researchers have found a key to the extreme diversity in dog size. Dogs descended from wolves about 15,000 years ago, but it is only in the past hundreds of years that the many different breeds have developed, encouraged by humans through selection.
Nathan B. Sutter and coauthors found that all small dogs share a specific sequence of DNA that is nearly absent from giant dog breeds. The DNA sequence includes the gene encoding insulin-like growth factor 1 (IGF1). Other researchers have found that IGF1 is related to body size in other organisms, including mice and humans.
The authors’ first research focused on Portuguese water dogs — a breed that has an unusually wide range of skeletal size. Eventually they studied the DNA analysis of more than 3,000 dogs from 143 breeds and found the same results. Next researchers will be identifying genes that contribute to other complex traits in dogs, such as behavior and disease.
Dr. Sutter and colleagues describe their findings in the 06 April 2007 issue of the journal Science.