What is southern blotting?

Southern blotting is a laboratory technique used to detect specific DNA sequences within a mixture of DNA molecules. In Southern blotting, genomic DNA is cut into fragments using restriction enzymes. These fragments are then separated by size on an agarose gel, where they become single-stranded. The separated DNA fragments are transferred onto a nylon or nitrocellulose membrane, forming a replica of the gel's pattern. A DNA probe, complementary to the target sequence, is applied to the membrane and allowed to hybridize. After washing off any unbound probes, the membrane is examined using a labeled tag, such as a chemical, fluorescent, or radioactive marker. This reveals the locations of the target DNA fragments. By comparing the fragment sizes to a known ladder and control samples, it helps identify any differences. If methylation detection is required, specific enzymes sensitive to methylation are used in the initial digestion. The resulting pattern of fragments can reveal whether an individual's DNA is methylated.