Caption

Gene mapping. Silhouetted male researcher examines a DNA autoradiogram during gene mapping studies. Banding patterns on the autoradiogram form a genetic fingerprint. By analysing the banding pattern he can determine the sequence of base pairs 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 size. The resulting banding pattern is preserved on X-ray film to produce this autoradiogram.