Stanford researchers sniff out gene that gives dogs...(t colors. Candille identified a region o...),Health

"Looking within one breed rapidly identifies the general region, but looking at different breeds allows you to home in on the gene that's responsible," Barsh said.

Candille's work narrowed the genome region to a gene that makes a beta-defensin protein, previously believed to play a role in fighting infection (hence the name). One version of the beta-defensin gene produces yellow dogs, a mutant version of the gene produces black. Co-first author Chris Kaelin, PhD, went on to prove it. When he inserted the dog gene in transgenic mice, their fur grew out black.

Though you wouldn't guess it looking at an Irish setter, all coat colors are modifications of black and yellow. "A Dalmatian looks white with black spots but based on its genetics it's black. Dogs that are chocolate - like one of my dogs, a chocolate poodle - are also a modification of black," said Barsh. However his other dog, an apricot poodle, is genetically yellow, as are Irish setters.

But the finding's relevance extends far beyond fur color. The beta-defensin gene is a member of the unusually large and variable defensin family of genes. A human can have between 40 and 50 different defensin genes; dogs can have up to 46.

Though researchers had assumed the defensin proteins were microbe fighters, Barsh isn't so sure.

"The most important observation that stems from the paper is that in trying to understand what defensins really do, we've been looking under a lamppost based on the way in which the gene family was named," said Barsh. "In fact, we really have very little evidence that defensins do much in terms of defending. The genetic approach is more agnostic, and suggests that defensins have additional or alternative functions outside the immune system."

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