Molecular geneticist loading samples onto an automated DNA sequencer.

Photograph taken at Great Ormond Street Hospital, London, May 2000. Increasingly, scientists are using machines to help them read DNA code. To read a genetic code, DNA fragments are tagged with fluorescent dyes: a different colour for each DNA letter. The fastest machines pull the different sized fragments through a very fine tube, or capillary. A laser beam then detects the moving, fluorescing DNA fragments as they pas.