FIGURE 1. Possible causes and consequences of uncontrolled movement of transposable elements ('jumping genes').

Red and green boxes represent silenced and active transposons, respectively. a, A transposable element in the genome is typically silenced by methylation (addition of CH₃ groups) and probably by repressive chromatin structures — certain modifications of the proteins that bundle up the genome (purple ovals). b, When these controls are disrupted — for example, in plants with the ddm1 mutation^{1, 2} — the transposon is expressed (represented by a wavy line) and jumps about the genome at a much higher rate. c, Possible consequences of the transposon jumping into new sites elsewhere in the genome, such as into or nearby other genes (open rectangles).