1) The separation of sequences or fragments of RNA, partially digested by endonucleases, on an electrophoretic gel.

2) A blot consisting of a sheet of cellulose nitrate or nylon that contains spots of RNA for identification by a suitable molecular probe.

3) Northern blot is a laboratory technique used to detect a specific RNA sequence in a blood or tissue sample. The sample RNA molecules are separated by size using gel electrophoresis. The RNA fragments are transferred out of the gel to the surface of a membrane. The membrane is exposed to a DNA probe labeled with a radioactive or chemical tag. If the probe binds to the membrane, then the complementary RNA sequence is present in the sample.