Roo element structure and phylogenetic tree of the 12 sequenced Drosophila species. a) The canonical roo element is 9092 basepairs (bp) long, has one 7083 bps long ORF (light gray box), and is flanked by 428/429 bps long LTR sequences (dark gray boxes). The ORF encodes the gag, pol and env genes. b) The phylogenetic tree of the Drosophila species is taken from . The number of identified roo and rooA elements is listed for each species. Roo and rooA elements are highlighted with red and blue bars, respectively.