False-colour transmission electron micrograph (TEM) of a circular loop or insplasmidins of bacterial DNA in which two individual genes (blue) have been mapped. The gene-mapping technique starts with an RNA copy of each gene, which is caused to anneal to one strand of the double-stranded bacterial DNA. This forms a discernible single-stranded loop, known as an insR-loopins (blue). The area where the RNA has annealed to one strand of the DNA (known as DNA/RNA hybrid) is coloured red. The ordinary double-stranded DNA is yellow. Magnification: x14,300 at 35mm size, x28,600 at 6x7cm size.