Cover image
Cover An ink drawing of monarch butterflies migrating through their genetically programmed “internal” landscape. Each fall, millions of monarchs migrate from eastern North America to their overwintering grounds in central Mexico. In this issue, a highly efficient gene-targeting approach, using zinc-finger nucleases, is used to define an essential transcriptional repressor as part of the genetic basis of the long-distance monarch migration, where an intact circadian clock is necessary for proper sun compass navigation. (Cover illustration by Vivian Budnik. [For details, see Merlin et al., pp. 159–168.])
