Cute dogs wowed our ancestors

APART from a yap out of proportion to their size, what do chihuahuas, terriers and pekinese have in common? The answer is a mutation in a single gene. The variant is found in so many small breeds that it must have been present early in the history of dogs' domestication.

A team led by Elaine Ostrander of the National Human Genome Research Institute in Bethesda, Maryland, looked at Portuguese water dogs, which come in an unusually wide range of sizes. The smaller dogs tended to carry a particular variant of the gene for the important growth regulator insulin-like growth factor 1 (IGF1) on chromosome 15. The team found the same variant in every small breed they investigated, but hardly ever in very large breeds such as St Bernards, Irish wolfhounds and Great Danes (Science, vol 316, p 112).

The "small" variant of IGF1 is not known in wolves -- dogs' closest wild relative. "Perhaps man selected a small wolf that doesn't exist now, or they found a small variant that everybody liked," says team member Gordon Lark at the University of Utah in Salt Lake City.