Practice question

Detection of radioactively labeled DNA fragments relies on emission of beta particles from isotopes such as 32P incorporated at termini. Gel electrophoresis separates fragments by size but does not detect radioactivity itself. Spectrometry and colorimetry measure absorbance or color development for quantification, not spatial band position. Autoradiography places dried gel against photographic film; radioactive decay exposes silver halide crystals producing dark bands corresponding precisely to labeled fragment migration positions. This method provides high sensitivity for low abundance labeled species in classical mapping before modern fluorescent labeling.