favored in a small region of southern Italy but less favored farther north or south. We propose that an origin of the derived ls-tim allele in southern Europe, followed by its subsequent spread by directional selection, providescounterintuitively-a more compelling model for understanding the elevated frequencies of ls-tim in this geographical region.

This study shows that, as in mammals, Drosophila CRY interacts with PER, and, as in plants, the C terminus of CRY is involved in mediating light responses. A model for the light dependence of CRY is discussed.