This technique shows the relationships between individuals: for example, it can be used to prove maternity or paternity of a child. The procedure is also used in FORENSIC MEDICINE whereby any tissue left behind by a criminal at the scene of a crime can be compared genetically with the tissue of a suspect. DNA, the genetic material in living cells, can be extracted from blood, semen and other body tissues. The technique, pioneered in Britain in 1984, is now widely used.