Genetic profiling is a forensic technique for identifying a person by comparing their DNA with that isolated from biological evidence found at a crime scene. Examples of such evidence are blood, semen, saliva, hair or skin and may only contain minute amounts of DNA. As PCR is very sensitive the risk of contamination increases and care must be taken to avoid contamination. First, the DNA sample is fragmented, amplified using PCR and separated using gel electrophoresis. The overall layout of the DNA fragments is called a DNA fingerprint.