Figure 7.

Model for propagation of SDR elements. The model follows the life cycle of an SDR element (white box). When a putative RNA-binding protein is present within the organism, the element is mobile and may insert into tandemly repeated sequences (tandem arrows), transposable elements (hatched box), or uncharacterized sequences (thin line). In the first two cases, the element may propagate to other sites in the genome even after the SDR element is no longer mobile. In the absence of selection, mutations (black boxes) accumulate in the element over time, giving rise to the diverse sequences observed in genomic sequences. See text for further explanation.