Distinguishing friends, foes, and freeloaders in giant genomes

Most annotations of large eukaryotic genomes initially find transposable elements (TEs) and other repeats, then mask them so that subsequent efforts can be concentrated on the annotation and study of non-TE genes. However, TEs often contribute to host biology, and their community biologies are of intrinsic interest. This review discusses the challenges, rationale and technologies for comprehensive TE annotation in the commonly giant genomes of animals and plants. Complete discovery of the TEs in a fully sequenced genome is laborious, but feasible, with current strategies in the hands of a careful researcher. These deep TE studies have begun to provide important perspectives on how genomes evolve and the degree to which genome changes do and do not affect eukaryotic biology.