This member of the gray squirrel species has black fur. (Image: © Shutterstock) Biologists from the United Kingdom think they’ve decoded the mystery of all the gray squirrels ( Sciurus carolinensis ) running around the United States with black fur. The bit of genetic code that causes the gray squirrel species to turn black, they showed, is an allele, or a variant form of a specific gene, called MC1R∆24. But that allele doesn’t seem to come from gray squirrels. Instead, they showed, the gray squirrel MC1R∆24 allele is "identical" to the MC1R∆24 allele found in another species, fox squirrels ( Sciurus niger ) — one of two mutations that occasionally cause big, usually reddish fox squirrels to turn black. In a paper published online July 11 in the journal BMC Evolutionary Biology , the researchers showed that the color-changing allele likely originated in fox squirrels and moved over to gray squirrels through interbreeding. To reach that conclusion, the researchers examined all three possible ways the gene variant could have turned up in both species. [ The 12 Biggest ‘Little’ Mysteries of Fall — Solved! ] "First, the allele could have arisen in the common ancestor of both species, and […]


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