Blotting techniques are widely used to separate and identify DNA, RNA, and proteins from a mixture by immobilizing the molecule of interest on a support membrane like nitrocellulose or nylon.

Southern blotting is used to detect specific sequences in DNA samples. Invented by Edwin Southern, it involves cutting large DNA molecules with restriction endonuclease. The fragments are separated by electrophoresis on an agar gel and transferred to a nitrocellulose membrane. The desired DNA is identified using a labeled probe through autoradiography.

Northern blotting is used to detect specific RNA molecules. Developed by Alwine, Kemp, and Stark, total RNA is extracted and separated on an agarose gel. The RNA is transferred to a positively charged nylon membrane because it has a high affinity for negatively charged nucleic acids. The buffer usually contains formamide to lower annealing temperatures and prevent RNA degradation.

Western blotting is used to detect specific proteins in a tissue homogenate. Coined by W. Neal Burnette, proteins are separated on SDS-PAGE gel based on electrophoretic mobility. They are transferred to a nitrocellulose membrane and detected using an antibody specific to the target protein.

Using these three techniques, one can identify a gene and its expression. Southern blotting identifies the gene in DNA, Northern blotting identifies the transcripts (RNA), and Western blotting identifies the protein expression from mRNA.