MAKING A MERLE: merle patterning--the presence of patches of light-colored fur--is a genetic trait seen in Australian Shepherds, Great Danes, Shetland Sheepdogs and several other dog breeds. It is also linked to ear and eye disorders in these animals. In a report published online this week by the Proceedings of the National Academy of Sciences scientists say they have unraveled the genetics of this trait. Apparently, merle dogs have a so-called retrotransposon--a mobile bit of DNA--in the middle of their SILV gene, which is responsible for pigmentation. The team notes that the finding could shed light on hearing and pigmentation disorders that affect both dogs and humans.