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DNA sequencing. Banded DNA sequences or genetic fingerprints on an autoradiogram. The pattern of bands represents the chemical sequence that forms the genetic code for a section of DNA (deoxyribonucleic acid). The DNA sample was cut into fragments by an enzyme and marked with radioactive tags. These fragments were then placed in a gel and separated by electrophoresis, the application of an electric charge. An autoradiogram of the resulting bands of radioactively-tagged DNA was made using radiographic film. DNA sequencing is used in forensic science, medical research and genealogy. (KEYSTONE/SCIENCE PHOTO LIBRARY/TEK IMAGE)