What type of radioactive isotope is commonly used in DNA labelling?
Radioisotopic labeling commonly uses phosphorus-32 because of its superior nuclear characteristics for nucleic acid detection. 32P is a high-energy beta emitter with a half-life of approximately 14.3 days, offering excellent sensitivity and short autoradiographic exposure times. It can be incorporated internally using [alpha-32P]dATP or dCTP during polymerization, or terminally as [gamma-32P]ATP via kinase reaction. Lower-energy isotopes like tritium, sulfur-35, and carbon-14 emit weak beta particles, require prolonged exposure, and provide poorer resolution. Hence 32P remains the isotope of choice for high-sensitivity probe labeling.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.