Molecular geneticist analysing the output of a DNA sequencer, May 2000.

Molecular geneticist analysing the output of an automated DNA sequencer, Great Ormond Street Hospital, London, May 2000. Increasingly, scientists are using machines to help them read DNA code. For automatic analysis, 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. This is much quicker than manual DNA sequencing.