The position and organisation of 5S insertions within the 26S-18S intergenic spacer. (A). The 26S, 18S and 5S genic regions are in green and red boxes, respectively. Mutated or incomplete 5S copies are indicated by vertical strips. The sizes of IGS1 are depicted with thin lines above the units. Direction of transcription is illustrated by thick arrows below the genes. Arrowheads indicate sequences homologous to terminal inverted repeats (TIR) of Cassandra elements, aligned in (B). (*) the IGS type with a single 5S gene is the most abundant in A. absinthium; (**) species with typical unlinked arrangement of units.