The differences between these 3 types of blots are described in your textbook. In a Southern blot, DNA restriction fragments are separated by gel electrophoresis, transferred to a membrane, and probed by hybridization with a specific cloned nucleic acid probe. A Northern blot is similar except that RNA molecules are separated by gel electrophoresis and transferred to a membrane. In the case of Western blots, protein molecules are separated by gel electrophoresis, transferred to a membrane, and probed with specific antibodies. Note that nucleic acids cannot hybridize with proteins.