Southern blot
Say it: SUTH-urn BLOT
A Southern blot is a laboratory method that finds a specific DNA sequence by separating DNA fragments on a gel, moving them to a membrane and probing them.
Also: Southern blotting, Southern hybridization
Definition
What is a Southern blot?
A Southern blot is a technique for detecting a particular DNA sequence within a complex mixture of DNA, such as a whole genome. The British biologist Edwin Southern invented it in 1975, and it carries his surname, which is why Southern is written with a capital S.
The DNA is first cut into fragments with one or more restriction enzymes, and the fragments are separated by size with gel electrophoresis. The gel is treated to separate the two strands of each fragment, and the DNA is then transferred, or blotted, onto a nylon or nitrocellulose membrane, keeping the same layout. The membrane is bathed in a labeled probe, a single-stranded piece of DNA complementary to the target, which base-pairs only with fragments carrying the matching sequence. A radioactive, fluorescent or chemical label then shows a band for each such fragment, and its position reveals the fragment's size.
Southern blots were central to early DNA fingerprinting, the study of restriction fragment length polymorphisms and gene mapping. PCR and sequencing have replaced them for most tasks, but they are still used to detect large deletions and rearrangements, to count gene copies and to size long repeat expansions, as in fragile X syndrome. The name inspired the Northern blot for RNA and the Western blot for proteins.
Practice it
Where you'll meet it
Quizzes that use it
Related
Terms that go with it
- Gel electrophoresisGel electrophoresis is a lab technique that uses an electric field to pull DNA, RNA or proteins through a gel, separating them by size.
- Restriction enzymeA restriction enzyme is a bacterial protein that cuts DNA at a specific short sequence, making it a basic tool for cutting and joining DNA.
- DNA profilingDNA profiling is a laboratory method that identifies a person from highly variable regions of their DNA, used in forensics and kinship testing.
- Western blotA Western blot is a laboratory method that detects a specific protein in a sample by separating proteins by size on a gel and probing them with antibodies.
- Polymerase chain reactionThe polymerase chain reaction (PCR) is a lab technique that copies one chosen stretch of DNA over and over until there are billions of copies.
- Copy number variationCopy number variation is a difference between people in how many copies of a given stretch of DNA their genomes carry, due to deletions or duplications.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- NHGRI Talking Glossary: Southern Blot
- OpenStax Biology 2e, 17.1 Biotechnology
- NCBI MeSH: Blotting, Southern
Last updated
Spotted a mistake? Tell us and we'll correct it.
Practice Molecular Biology
Free molecular biology quizzes, with an explanation for every answer.
See the Quizzes