False-colour transmission electron micrograph of a DNA transposable genetic element (a transposon), forming a characteristic stem-&-loop structure. Transposons are discrete segments of DNA that move around chromosomes joining together DNA segments that have no structural or ancestral relationship to each other. Their ability to recombine with dissimilar DNA segments gives rise to mutations, which in turn increases the diversity of genetic material available. They represent a mechanism for evolutionary change among biological systems. Mag: x40,000 at 35mm size.