Editing Griffith's experiment

{{Short description|Experiment demonstrating transfer of genetic information}}
[[Image:Griffith experiment.svg|thumb|450px|right|Griffith's experiment discovering the "transforming principle" in [[Streptococcus pneumoniae|Streptococcus pneumoniae (pneumococcal) bacteria.]]]]

'''Griffith's experiment''',<ref>{{Cite book|url=http://dx.doi.org/10.21428/cdd5dd5a|title=Experiment|publisher=PubPub|doi=10.21428/cdd5dd5a}}</ref> performed by [[Frederick Griffith]] and reported in 1928,<ref>{{cite journal |last=Griffith|first=Fred.|author-link=Frederick Griffith|title=The Significance of Pneumococcal Types|journal=Journal of Hygiene |publisher=Cambridge University Press|date=January 1928|volume=27|issue=2|pages=113–159|jstor=4626734 |pmid=20474956 |pmc=2167760 |doi=10.1017/S0022172400031879}}</ref> was the first experiment suggesting that bacteria are capable of transferring genetic information through a process known as [[Transformation (genetics)|transformation]].<ref>{{cite journal|last1=Lorenz|first1=M. G.|last2=Wackernagel|first2=W.|title=Bacterial gene transfer by natural genetic transformation in the environment|journal=[[Microbiology and Molecular Biology Reviews|Microbiological Reviews]]|volume=58 |issue=3|pages=563–602 |date=1994-09-01 |pmid=7968924|pmc=372978 |doi=10.1128/MMBR.58.3.563-602.1994}}</ref><ref>{{cite journal|last=Downie|first=A. W.|title=Pneumococcal transformation — a backward view: Fourth Griffith Memorial Lecture|journal=[[Microbiology (journal)|Journal of General Microbiology]]|url=http://mic.sgmjournals.org/content/73/1/1.full.pdf |archive-url=https://web.archive.org/web/20120302055304/http://mic.sgmjournals.org/content/73/1/1.full.pdf |archive-date=2012-03-02 |url-status=live|volume=73|issue=1|pages=1–11|year=1972|doi=10.1099/00221287-73-1-1|pmid=4143929|access-date=2011-11-30|doi-access=free}}</ref>  Griffith's findings were followed by [[Avery–MacLeod–McCarty experiment|research in the late 1930s and early 40s]] that isolated [[DNA]] as the material that communicated this genetic information.

[[Pneumonia]] was a serious cause of death in the wake of the [[1918 flu pandemic|post-WWI Spanish influenza pandemic]], and Griffith was studying the possibility of creating a [[vaccine]].  Griffith used two [[Strain (biology)|strain]]s of pneumococcus (''[[Diplococcus pneumoniae]]'') bacteria which infect [[mouse|mice]] – a type III-S (smooth) which was [[virulent]], and a type II-R (rough) strain which was nonvirulent. The III-S strain synthesized a [[polysaccharide]] capsule that protected itself from the host's [[immune system]], resulting in the death of the host, while the II-R strain did not have that protective capsule and was defeated by the host's immune system. A German bacteriologist, [[Fred Neufeld]], had discovered the three pneumococcal types (Types I, II, and III) and discovered the [[quellung reaction]] to identify them ''in vitro''.<ref>{{cite book| url = https://books.google.com/books?id=iwDn7ubDO2kC| title = Lehrer, Steven. Explorers of the Body. 2nd edition 2006 p 44| isbn = 9780595407316| last1 = Lehrer| first1 = Steven| year = 2006| publisher = iUniverse}}</ref> Until Griffith's experiment, bacteriologists believed that the types were fixed and unchangeable, from one generation to another.

In this experiment, [[bacterium|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.

Scientific advances since then have revealed that the "transforming principle" Griffith observed was the [[DNA]] of 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 smooth 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–MacLeod–McCarty experiment|Avery, McLeod and McCarty]] and by [[Hershey–Chase experiment|Hershey and Chase]].

==Notes==
{{Reflist}}

==References==
*{{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 = 137–158 | year = 1944 | doi = 10.1084/jem.79.2.137 | pmid=19871359 | pmc=2135445}}
::(References the original experiment by Griffith. [http://osulibrary.oregonstate.edu/specialcollections/coll/pauling/dna/papers/avery.html Original article] and [https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=33226 35th anniversary reprint] available.'')

==Further reading==
* {{cite book |author1=Daniel Hartl |author2=Elizabeth Jones | title=Genetics: Analysis of Genes and Genomes, 6th edition | publisher=Jones & Bartlett | year = 2005}} 854 pages. {{ISBN|0-7637-1511-5}}
*{{cite book | last = Lehrer | first = Steven | title = Explorers of the Body | url = https://books.google.com/books?id=iwDn7ubDO2kC | publisher = iUniverse, Inc | location = United States | year = 2006 | isbn = 0-595-40731-5 |edition=2nd}}
{{History of biology}}

{{DEFAULTSORT:Griffith's Experiment}}
[[Category:Genetics experiments]]
[[Category:Genetics in the United Kingdom]]
[[Category:History of genetics]]
[[Category:Microbiology]]
[[Category:1928 in biology]]