Blot methods in laboratory diagnosis: Southern blot, Western blot, Northern blot, etc.

Author: V. Dimov, M.D., Allergist/Immunologist and Assistant Professor at University of Chicago
Reviewer: S. Randhawa, M.D., Allergist/Immunologist and Assistant Professor at NSU

In basic science, a blot is a method of transferring proteins, DNA, or RNA onto a carrier. The following types are known:

- Southern blot to recognize DNA (used to detect TRECs in SCID diagnosis). Population-based screening for SCID in neonates: The winner is T-cell receptor excision circles. JACI, 2012. See the TRECs figure here:

- Northern blot to recognize RNA

- Western blot to recognize proteins (used for HIV diagnosis)

- Eastern blot to recognize posttranslational modifications


Logically, the whole process starts with DNA (and Southern blot was discovered first), then RNA, protein, and finally, posttranslational modification.

South -> North -> West

Other blots

- Southwestern blot for protein-DNA
- Far-Western blot for protein-protein
- Far-Eastern blot for lipids, drugs and hormones

A Southern blot is a method routinely used in molecular biology for detection of a specific DNA sequence in DNA samples. The method is named after its inventor, the British biologist Edwin Southern. Other blotting methods (i.e., Western blot, Northern blot, Eastern blot, Southwestern blot) that employ similar principles, but using RNA or protein, have later been named in reference to Edwin Southern's name. As the technique was eponymously named, Southern blot should be capitalized as is required for proper nouns, whereas names for other blotting methods should not.

Severe combined immunodeficiency (SCID) - 4 groups according to T/B/NK cells (click to enlarge the image).

Fluorescent in situ hybridization (FISH)

Fluorescent in situ hybridization (FISH) is used to detect the presence or absence of specific DNA sequences. DiGeorge syndrome is diagnosed by FISH (22q11.2 deletion).


Southern, E.M. (1975): "Detection of specific sequences among DNA fragments separated by gel electrophoresis", J Mol Biol., 98:503-517. PMID 1195397.
Southern blot. Wikipedia.

Published: 05/14/2010
Updated: 03/07/2012

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