Schematic diagram of the location, size and structure of copies of the SR3 non-LTR retrotransposon in bacterial artificial chromosome number 49_J_14 from chromosome 1 of the genome of Schistosoma mansoni. The location of copies of the SR2 and fugitive retrotransposons is also presented. The arrows indicate the direction of transcription of the mobile elements. The numbers on each bar indicate the nucleotide position of the elements within the bacterial artificial chromosome. A degenerate copy of the SR2 element was evident within intron 1 of Zn-Cu superoxide dismutase (SOD) gene, in particular within intron 1 of the gene: three exons of the SOD are indicated in red, with the position and structure of the degenerate copy of SR2 indicated within intron 1. On the bottom right, a schematic of the length and domain structure of the SR3-right copy of the SR3 retrotransposon is presented. RT, reverse transcriptase; EN, endonuclease.