Although the DNA from different individuals is more alike than different, there are many regions of human chromosomes that exhibit a great deal of diversity. Such variable sequences are termed “polymorphic” (meaning many forms) and provide the basis for forensic identification. This experiment uses gel electrophoresis and a DNA chip to examine a highly variable locus within the human genome, like the ones used by the FBI for DNA fingerprinting. This locus, D1S80, contains a variable number of tandem repeats, which can be used to build an individual's unique DNA profile. In this first part of the experiment, join DNALC educator Jeffry Petracca as he demonstrates how to extract and purify DNA from cheek cells using saline mouthwash, and amplify the D1S80 locus by PCR.