MODEL RELEASED. Gene mapping. Male scientist studies a series of DNA sequencing autoradiograms or genetic fingerprints" through a magnifying glass. He is determining the sequence of base pairs (cytosine, guanine, adenine, thymine) that form the code for a section of DNA. A sample of DNA has been cut into fragments by an enzyme and marked with a radioactive tag for sequencing. The DNA fragments are then separated by electrophoresis in an agarose gel, moving different distances along the gel according to their size. The resulting banding pattern, as seen here, is preserved by applying a radiographic film to produce these autoradiograms."