Southern Blot
Definition
A technique (E.M. Southern, 1975) in which restriction-digested DNA fragments are separated by gel electrophoresis, transferred to a membrane, and hybridised with a labelled probe to detect specific sequences at defined molecular weights. The first forensic DNA fingerprinting method (Jeffreys, 1984) used this technique.
- Developer
- E.M. Southern, 1975
- Steps
- Restriction digest, gel electrophoresis, membrane transfer, probe hybridisation
- Forensic milestone
- Basis of the first forensic DNA fingerprinting method, Jeffreys 1984
- Detects
- Specific sequences at defined molecular weights
Common questions
Why is Southern blotting no longer the standard forensic DNA method today?+
It requires relatively large amounts of intact, high molecular weight DNA and takes days to complete, whereas PCR-based STR typing needs only tiny or degraded samples and produces results far faster, so Southern blot based RFLP typing was replaced by STR analysis in routine forensic casework from the 1990s onward.
How does Southern blot relate to Northern and Western blots mentioned alongside it?+
All three follow the same transfer-and-probe logic, but Southern blot detects DNA, Northern blot detects RNA, and Western blot detects protein, with the naming a play on Southern's original surname extended by convention to the other molecule types.
Related terms
- Microarray (Gene Chip / SNP Chip)
- A solid-phase hybridisation platform carrying thousands to millions of oligonucleotide probes at spatially registered positions. Hybridisation of a labelled target simultaneously queries...
- Minisatellite (VNTR)
- A hypervariable genomic locus characterised by tandem repeats of a 10-60 bp core sequence, with the number of repeat units varying between...
- Molecular Hybridisation
- The formation of a double-stranded nucleic acid molecule from two complementary single strands, driven by hydrogen-bond formation between base pairs (A-T, G-C...
- mRNA Body-Fluid Profiling
- The RT-PCR-based descendant of Northern blotting: tissue-specific messenger RNA transcripts are reverse-transcribed and amplified from crime-scene stains to identify body fluid of...
- Stringency
- The extent to which hybridisation conditions favour only perfectly complementary probe-target pairs over partially mismatched ones. High stringency (elevated temperature and/or low...
- Western Blot (Protein Immunoblot)
- SDS-polyacrylamide gel electrophoresis (SDS-PAGE) of proteins followed by electrotransfer to a PVDF or nitrocellulose membrane, then antibody-based detection of a specific protein...