- Griffith's experiment
Griffith's experiment, conducted in 1928 by
Frederick Griffith, was one of the first experiments suggesting that bacteria are capable of transferring genetic information through a process known as transformation. [cite journal |author=Lorenz MG, Wackernagel W |title=Bacterial gene transfer by natural genetic transformation in the environment |journal=Microbiol. Rev. |volume=58 |issue=3 |pages=563–602 |year=1994 |pmid=7968924 |url=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=7968924] [cite journal |author=Downie AW |title=Pneumococcal transformation--a backward view. Fourth Griffith Memorial Lecture |journal=J. Gen. Microbiol. |volume=73 |issue=1 |pages=1–11 |year=1972 |pmid=4143929]
Griffith used two strains of "
Pneumococcus" (which infects mice), a type III-S (smooth) and type II-R (rough) strain. The III-S strain covers itself with a polysaccharidecapsule that protects it from the host's immune system, resulting in the death of the host, while the II-R strain doesn't have that protective capsule and is defeated by the host's immune system.
In this experiment, bacteria from the III-S strain were killed by heat, and their remains were added to II-R strain bacteria. While neither alone harmed the mice, the combination was able to kill its host. Griffith was also able to isolate both live II-R and live III-S strains of "pneumococcus" from the blood of these dead mice. Griffith concluded that the type II-R had been "transformed" into the lethal III-S strain by a "transforming principle" that was somehow part of the dead III-S strain bacteria.
Today, we know that the "transforming principle" Griffith observed was the
DNAof the III-S strain bacteria. While the bacteria had been killed, the DNA had survived the heating process and was taken up by the II-R strain bacteria. The III-S strain DNA contains the genes that form the protective polysaccharide capsule. Equipped with this gene, the former II-R strain bacteria were now protected from the host's immune system and could kill the host. The exact nature of the transforming principle (DNA) was verified in the experiments done by Avery, McLeod and McCarty and by Hershey and Chase.
*cite journal | author = Avery, MacLeod, and McCarty | title = Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types: Induction of Transformation by a Desoxyribonucleic Acid Fraction Isolated from Pneumococcus Type III | journal = Journal of Experimental Medicine | volume = 79 | issue = 1 | pages = 137–58 | year = 1944 | doi = 10.1084/jem.79.2.137 ::(References the original experiment by Griffith. [http://osulibrary.oregonstate.edu/specialcollections/coll/pauling/dna/papers/avery.html Original article] and [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=33226 35th anniversary reprint] available.")
* cite book
author = Daniel Hartl and Elizabeth Jones
title=Genetics: Analysis of Genes and Genomes, 6th edition
publisher=Jones & Bartlett
year = 2005 854 pages. ISBN 0-7637-1511-5.
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