Intro to Biotechnology Mark Muller March 19, 2015 Chelsea Claverie Midterm Study Guide The Northern Blot detects the presence of certain RNA sequences, while the Southern blot can detect various DNA segments. Northern blot uses a gel electrophoresis, blot, RNA probes, and x-ray to determine the presence of a particular mRNA sequence that was immobilized and run in the electrophoresis. Southern blot uses an autoradiograph in combination with an electrophoresis gel to identify similarities between DNA. Similar DNA should travel the same distance in the electrophoresis, on the blot, and have the same binding sites from probes on the autoradiograph.