Direct hybridization of labeled DNA to DNA in agarose gels

A fast and simple procedure for the hybridization of radioactive probes directly to DNA in agarose gels is described. Restriction endonuclease-digested DNA is fractionated by electrophoresis in agarose gel. After drying, the DNA in the gel is denatured with alkali and annealed with a radioactive probe, and the hybridization pattern visualized by autoradiography. This method is sensitive enough to detect single or low copy number DNA sequences in the genome of higher eucaryotes.