Editing Mutagen

{{Short description|Physical or chemical agent that increases the rate of genetic mutation}}
{{More footnotes needed|date=April 2023}}
[[File:GHS-pictogram-silhouette.svg|thumb|The [[Globally Harmonized System of Classification and Labeling of Chemicals|international]] [[GHS hazard pictograms|pictogram]] for chemicals that are sensitising, mutagenic, [[carcinogen]]ic or [[Reproductive toxicity|toxic to reproduction]]]]

In [[genetics]], a '''mutagen''' is a physical or chemical agent that permanently changes [[nucleic acid|genetic material]], usually [[DNA]], in an [[organism]] and thus increases the frequency of [[mutation]]s above the natural background level. As many mutations can cause [[cancer]] in animals, such mutagens can therefore be [[carcinogen]]s, although not all necessarily are. All mutagens have characteristic [[mutational signatures]] with some chemicals becoming mutagenic through cellular processes.

The process of DNA becoming modified is called [[mutagenesis]]. Not all mutations are caused by mutagens: so-called "spontaneous mutations" occur due to spontaneous [[hydrolysis]], [[DNA error|errors]] in [[DNA replication]], repair and [[Genetic recombination|recombination]].

==Discovery==
The first mutagens to be identified were [[carcinogen]]s, substances that were shown to be linked to [[cancer]]. [[Tumor]]s were described more than 2,000 years before the discovery of [[chromosome]]s and [[DNA]]; in 500 B.C., the Greek [[physician]] [[Hippocrates]] named tumors resembling a crab ''karkinos'' (from which the word "cancer" is derived via Latin), meaning crab.<ref>{{cite journal | vauthors = Papavramidou N, Papavramidis T, Demetriou T | title = Ancient Greek and Greco-Roman methods in modern surgical treatment of cancer | journal = Annals of Surgical Oncology | volume = 17 | issue = 3 | pages = 665–7 | date = March 2010 | pmid = 20049643 | pmc = 2820670 | doi = 10.1245/s10434-009-0886-6 }}</ref> In 1567, Swiss physician [[Paracelsus]] suggested that an unidentified substance in mined ore (identified as [[radon]] gas in modern times) caused a wasting disease in miners,<ref name="Luch Nature and nurture">{{cite journal |last1=Luch |first1=Andreas |title=Nature and nurture – lessons from chemical carcinogenesis |journal=Nature Reviews Cancer |date=February 2005 |volume=5 |issue=2 |pages=113–125 |doi=10.1038/nrc1546 |pmid=15660110 }}</ref> and in England, in 1761, [[John Hill (author)|John Hill]] made the first direct link of cancer to chemical substances by noting that excessive use of [[snuff (tobacco)|snuff]] may cause nasal cancer.<ref>{{Cite book|url=http://resource.nlm.nih.gov/2166041R|title=Cautions against the immoderate use of snuff: founded on the known qualities of the tobacco plant: and the effects it must produce when this way taken into the body: and enforced by instances of persons who have perished miserably of diseases, occasioned, or rendered incurable by its use|last=Hill|first=John|publisher=Printed for Baldwin R and Jackson J|year=1761|location=London|name-list-style=vanc}}</ref> In 1775, Sir [[Percivall Pott]] wrote a paper on the high incidence of scrotal cancer in [[chimney sweep]]s, and suggested chimney [[soot]] as the cause of scrotal cancer.<ref>{{cite journal | vauthors = Brown JR, Thornton JL | title = Percivall Pott (1714-1788) and chimney sweepers' cancer of the scrotum | journal = British Journal of Industrial Medicine | volume = 14 | issue = 1 | pages = 68–70 | date = January 1957 | pmid = 13396156 | pmc = 1037746 | doi = 10.1136/oem.14.1.68 }}</ref> In 1915, Yamagawa and Ichikawa showed that repeated application of coal tar to rabbit's ears produced malignant cancer.<ref>{{cite journal|vauthors=Yamagawa K, Ichikawa K|year=1915|title=Experimentelle Studie über die Pathogenese der Epithelialgeschwülste|journal=Mitteilungen aus der Medizinischen Fakultät der Kaiserlichen Universität zu Tokyo|volume=15|pages=295–344|doi=10.11501/1675887}}</ref> Subsequently, in the 1930s the carcinogen component in coal tar was identified as a [[Polycyclic aromatic hydrocarbon|polyaromatic hydrocarbon]] (PAH), [[benzo(a)pyrene|benzo[a]pyrene]].<ref name="Luch Nature and nurture"/><ref>{{cite journal|vauthors=Cook JW, Hewett CL, Hieger I|year=1933|title=The isolation of a cancer-producing hydrocarbon from coal tar|journal=[[Journal of the Chemical Society|J. Chem. Soc.]]|volume=24|pages=395–405|doi=10.1039/JR9330000395|df=dmy-all}}</ref> Polyaromatic hydrocarbons are also present in soot, which was suggested to be a causative agent of cancer over 150 years earlier.

The association of exposure to radiation and cancer had been observed as early as 1902, six years after the discovery of X-ray by [[Wilhelm Röntgen]] and radioactivity by [[Henri Becquerel]].<ref>{{cite journal|vauthors=Kathren RL|date=Dec 2002|title=Historical Development of the Linear Nonthreshold Dose-Response Model as Applied to Radiation|url=https://scholars.unh.edu/unh_lr/vol1/iss1/5/|journal=University of New Hampshire Law Review|volume=1|issue=1}}</ref> [[Georgii Nadson]] and German Filippov were the first who created fungi mutants under [[ionizing radiation]] in 1925.<ref>{{Cite news|url=https://scfh.ru/en/papers/quot-russian-trail-quot-in-the-discovery-of-dna-structure/|title="Russian Trail" in the Discovery of DNA Structure|date=2004|work=SCIENCE First Hand|archive-url=https://web.archive.org/web/20170818090349/https://scfh.ru/en/papers/quot-russian-trail-quot-in-the-discovery-of-dna-structure/|archive-date=18 August 2017|url-status=live|publisher=INFOLIO|issue=N2|volume=3}}</ref><ref>{{cite book|title=Bericht über das Jahr 1960|vauthors=Böhme H|publisher=Springer Verlag|year=1961|isbn=978-3-642-94811-4|veditors=Bünning E, Gäumann E|volume=23|location=Berlin|pages=502–509|language=de|chapter=Angewandte Mikrobiologie|doi=10.1007/978-3-642-94810-7_40|quote=Bereits kurz nach der Entdeckung der Möglichkeit einer Auslösung von Mutationen durch ionisierende Strahlen (Nadson u. Filippov 1925, 1928; Muller 1927)}}</ref> The mutagenic property of mutagens was first demonstrated in 1927, when [[Hermann Joseph Muller|Hermann Muller]] discovered that [[x-ray]]s can cause genetic mutations in [[Drosophila melanogaster|fruit flies]], producing [[phenotype|phenotypic]] mutants as well as observable changes to the chromosomes,<ref name="Calabrese Nobel lecture">{{cite journal |last1=Calabrese |first1=Edward J. |title=Muller's Nobel lecture on dose–response for ionizing radiation: ideology or science? |journal=Archives of Toxicology |date=December 2011 |volume=85 |issue=12 |pages=1495–1498 |doi=10.1007/s00204-011-0728-8 |pmid=21717110 |bibcode=2011ArTox..85.1495C }}</ref><ref>{{cite journal |last1=Muller |first1=H. J. |title=Artificial Transmutation of the Gene |journal=Science |date=22 July 1927 |volume=66 |issue=1699 |pages=84–87 |doi=10.1126/science.66.1699.84 |pmid=17802387 |bibcode=1927Sci....66...84M }}</ref> visible due to the presence of enlarged [[Polytene chromosome|"polytene" chromosomes]] in fruit fly salivary glands.<ref>{{cite book|title=Introduction to Genetic Analysis|last1=Griffiths|first1=Anthony J. F.|last2=Wessler|first2=Susan R.|last3=Carroll|first3=Sean B.|last4=Doebley|first4=John|date=2012|publisher=W. H. Freeman|isbn=978-1-4292-7634-4|edition=10th|page=255|name-list-style=vanc}}</ref> His collaborator [[Edgar Altenburg]] also demonstrated the mutational effect of UV radiation in 1928.<ref>{{Cite journal|vauthors=Altenburg E|date=1928|title=The Limit of Radiation Frequency Effective in Producing Mutations|journal=[[The American Naturalist|Am. Nat.]]|volume=62|issue=683|pages=540–545|jstor=2457052|doi=10.1086/280230|bibcode=1928ANat...62..540A |s2cid=83653780}}</ref> Muller went on to use x-rays to create [[Drosophila]] mutants that he used in his studies of [[genetics]].<ref>{{cite journal | vauthors = Crow JF, Abrahamson S | title = Seventy years ago: mutation becomes experimental | journal = Genetics | volume = 147 | issue = 4 | pages = 1491–6 | date = December 1997 | doi = 10.1093/genetics/147.4.1491 | pmid = 9409815 | pmc = 1208325 }}</ref> He also found that X-rays not only mutate [[gene]]s in fruit flies,<ref name="Calabrese Nobel lecture"/> but also have effects on the genetic makeup of humans.<ref>{{cite book|title=Biology|vauthors=Campbell NA, Reece JB|publisher=Pearson Education, Inc|year=2005|isbn=978-0-8053-7146-8|edition=7th|location=San Francisco, CA}}</ref>{{better source needed|date=July 2017}} Similar work by [[Lewis Stadler]] also showed the mutational effect of X-rays on barley in 1928,<ref>{{cite journal | vauthors = Stadler LJ | title = Mutations in Barley Induced by X-Rays and Radium | journal = Science | volume = 68 | issue = 1756 | pages = 186–7 | date = August 1928 | pmid = 17774921 | doi = 10.1126/science.68.1756.186 | bibcode = 1928Sci....68..186S }}</ref> and [[ultraviolet]] (UV) radiation on maize in 1936.<ref name="stadler">{{cite journal | vauthors = Stadler LJ, Sprague GF | title = Genetic Effects of Ultra-Violet Radiation in Maize: I. Unfiltered Radiation | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 22 | issue = 10 | pages = 572–8 | date = October 1936 | pmid = 16588111 | pmc = 1076819 | doi = 10.1073/pnas.22.10.572 | bibcode = 1936PNAS...22..572S | author-link1 = Lewis Stadler | doi-access = free }}</ref> The effect of sunlight had previously been noted in the nineteenth century where rural outdoor workers and sailors were found to be more prone to skin cancer.<ref>{{cite journal |last1=Hockberger |first1=Philip E. |title=A History of Ultraviolet Photobiology for Humans, Animals and Microorganisms |journal=Photochemistry and Photobiology |date=May 2007 |volume=76 |issue=6 |pages=561–579 |doi=10.1562/0031-8655(2002)0760561AHOUPF2.0.CO2 }}</ref>

[[Chemical mutagen]]s were not demonstrated to cause mutation until the 1940s, when [[Charlotte Auerbach]] and [[J. M. Robson]] found that [[mustard gas]] can cause [[mutation]]s in fruit flies.<ref>{{cite journal | vauthors = Auerbach C, Robson JM, Carr JG | title = The Chemical Production of Mutations | journal = Science | volume = 105 | issue = 2723 | pages = 243–7 | date = March 1947 | pmid = 17769478 | doi = 10.1126/science.105.2723.243 | bibcode = 1947Sci...105..243A | author-link = Charlotte Auerbach }}</ref> A large number of chemical mutagens have since been identified, especially after the development of the [[Ames test]] in the 1970s by [[Bruce Ames]] that screens for mutagens and allows for preliminary identification of carcinogens.<ref>{{cite journal | vauthors = Ames BN, Lee FD, Durston WE | title = An improved bacterial test system for the detection and classification of mutagens and carcinogens | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 70 | issue = 3 | pages = 782–6 | date = March 1973 | pmid = 4577135 | pmc = 433358 | doi = 10.1073/pnas.70.3.782 | bibcode = 1973PNAS...70..782A | doi-access = free }}</ref><ref>{{cite journal | vauthors = Ames BN | title = Identifying environmental chemicals causing mutations and cancer | journal = Science | volume = 204 | issue = 4393 | pages = 587–93 | date = May 1979 | pmid = 373122 | doi = 10.1126/science.373122 | bibcode = 1979Sci...204..587A | jstor = 1748159 | author-link = Bruce Ames }}</ref> Early studies by Ames showed around 90% of known carcinogens can be identified in Ames test as mutagenic (later studies however gave lower figures),<ref>{{cite journal | vauthors = McCann J, Choi E, Yamasaki E, Ames BN | title = Detection of carcinogens as mutagens in the Salmonella/microsome test: assay of 300 chemicals | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 72 | issue = 12 | pages = 5135–9 | date = December 1975 | pmid = 1061098 | pmc = 388891 | doi = 10.1073/pnas.72.12.5135 | bibcode = 1975PNAS...72.5135M | display-authors = 3 | doi-access = free }}</ref><ref>{{cite journal |last1=McCann |first1=Joyce |last2=Swirsky Gold |first2=Lois |last3=Horn |first3=Laura |last4=McGill |first4=R. |last5=Graedel |first5=T.E. |last6=Kaldor |first6=John |title=Statistical analysis of Salmonella test data and comparison to results of animal cancer tests |journal=Mutation Research/Genetic Toxicology |date=January 1988 |volume=205 |issue=1–4 |pages=183–195 |doi=10.1016/0165-1218(88)90017-1 |pmid=3285186 }}</ref><ref name="dunkel"/> and ~80% of the mutagens identified through Ames test may also be carcinogens.<ref name="dunkel">{{cite journal | vauthors = Dunkel VC, Zeiger E, Brusick D, McCoy E, McGregor D, Mortelmans K, Rosenkranz HS, Simmon VF | title = Reproducibility of microbial mutagenicity assays: II. Testing of carcinogens and noncarcinogens in Salmonella typhimurium and Escherichia coli | journal = Environmental Mutagenesis | volume = 7 Suppl 5 | issue = suppl. 5 | pages = 1–248 | year = 1985 | pmid = 3905369 | display-authors = 3 | doi = 10.1002/em.2860070902 }}</ref><ref>{{cite journal | vauthors = Benigni R, Bossa C | title = Alternative strategies for carcinogenicity assessment: an efficient and simplified approach based on in vitro mutagenicity and cell transformation assays | journal = Mutagenesis | volume = 26 | issue = 3 | pages = 455–60 | date = May 2011 | pmid = 21398403 | doi = 10.1093/mutage/ger004 | doi-access = free }}</ref>

==Difference between mutagens and carcinogens==
Mutagens are not necessarily carcinogens, and vice versa. [[Sodium azide]] for example may be mutagenic (and highly toxic), but it has not been shown to be carcinogenic.<ref>{{cite web|url=http://ntp.niehs.nih.gov/ntp/htdocs/lt_rpts/tr389.pdf|title=Toxicology And Carcinogenesis Studies Of Sodium Azide in F344/N Rats|date=1991|website=nih.gov|publisher=[[National Institutes of Health|NIH]]|type=technical report|archive-url=https://web.archive.org/web/20111023165026/http://ntp.niehs.nih.gov/ntp/htdocs/LT_rpts/tr389.pdf|archive-date=23 October 2011|url-status=live}}</ref> Meanwhile, compounds which are not directly mutagenic but stimulate cell growth which can reduce the effectiveness of DNA repair and indirectly increase the chance of mutations, and therefore that of cancer.<ref>{{Cite book |last1=Hill |first1=John |url=https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Chemistry_for_Changing_Times_(Hill_and_McCreary) |title=Chemistry for Changing Times |last2=McCreary |first2=John |publisher=[[Pearson PLC|Pearson]] |year=2019 |isbn=978-0-13-498863-4 |edition=15 |language=en |chapter=22.6 Carcinogens and Teratogens |doi=10.1021/ed050pa44.2 |chapter-url=https://chem.libretexts.org/@go/page/152300}}</ref> One example of this would be [[anabolic steroid]]s, which stimulate growth of the prostate gland and increase the risk of [[prostate cancer]] among others.<ref>{{Cite journal |last1=Salerno |first1=Monica |last2=Cascio |first2=Orazio |last3=Bertozzi |first3=Giuseppe |last4=Sessa |first4=Francesco |last5=Messina |first5=Antonietta |last6=Monda |first6=Vincenzo |last7=Cipolloni |first7=Luigi |last8=Biondi |first8=Antonio |last9=Daniele |first9=Aurora |last10=Pomara |first10=Cristoforo |date=2018-04-10 |title=Anabolic androgenic steroids and carcinogenicity focusing on Leydig cell: a literature review |journal=Oncotarget |volume=9 |issue=27 |pages=19415–19426 |doi=10.18632/oncotarget.24767 |issn=1949-2553 |pmc=5922407 |pmid=29721213}}</ref> Other carcinogens may cause cancer through a variety of mechanisms without producing mutations, such as [[tumour promotion]], [[immunosuppression]] that reduces the ability to fight cancer cells or pathogens that can cause cancer, disruption of the [[endocrine system]] (e.g. in breast cancer), tissue-specific toxicity, and [[inflammation]] (e.g. in colorectal cancer).<ref>{{cite journal |title=Mechanisms of non-genotoxic carcinogens and importance of a weight of evidence approach|author=Lya G. Hernández |author2=Harry van Steeg |author3=Mirjam Luijten |author4=Jan van Benthem |journal=Mutation Research/Reviews in Mutation Research |volume =682| issue =2–3|date= 2009| pages= 94–109 |doi=10.1016/j.mrrev.2009.07.002 |pmid=19631282|bibcode=2009MRRMR.682...94H }}</ref>

==Difference between mutagens and DNA damaging agents==

A [[DNA damage (naturally occurring)|DNA damaging agent]] is an agent that causes a change in the structure of DNA that is not itself replicated when the [[DNA replication|DNA is replicated]].<ref name = Bernstein1991>Bernstein, C.; Bernstein, H. (1991). Aging, Sex, and DNA Repair. pgs. 15-16. San Diego: Academic Press. {{ISBN|978-0-12-092860-6}}</ref>  Examples of DNA damage include a chemical addition or disruption of a [[nucleotide]] base in DNA (generating an abnormal nucleotide or nucleotide fragment), or a break in one or both strands in DNA.  When duplex DNA containing a damaged base is replicated, an incorrect base may be inserted in the newly synthesized strand opposite the damaged base in the complementary template strand, and this can become a [[mutation]] in the next round of replication.  Also a DNA double-strand break may be repaired by an inaccurate process leading to an altered base pair, a mutation.  However, mutations and DNA damages differ in a fundamental way: mutations can, in principle, be replicated when DNA replicates, whereas DNA damages are not necessarily replicated.  Thus DNA damaging agents often cause mutations as a secondary consequence, but not all DNA damages lead to mutation and not all mutations arise from a DNA damage.<ref name = Bernstein1991/>  The term genotoxic means toxic (damaging) to DNA.

==Effects==
{{main|Mutagenesis }}
Mutagens can cause changes to the DNA and are therefore [[Genotoxicity|genotoxic]]. They can affect the transcription and replication of the DNA, which in severe cases can lead to cell death. The mutagen produces mutations in the DNA, and deleterious mutation can result in aberrant, impaired or loss of function for a particular gene, and accumulation of mutations may lead to cancer. Mutagens may therefore be also carcinogens. However, some mutagens exert their mutagenic effect through their metabolites, and therefore whether such mutagens actually become carcinogenic may be dependent on the metabolic processes of an organism, and a compound shown to be mutagenic in one organism may not necessarily be carcinogenic in another.<ref>{{cite journal | vauthors = Allen JW, DeWeese GK, Gibson JB, Poorman PA, Moses MJ | title = Synaptonemal complex damage as a measure of chemical mutagen effects on mammalian germ cells | journal = Mutation Research | volume = 190 | issue = 1 | pages = 19–24 | date = January 1987 | pmid = 3099192 | doi = 10.1016/0165-7992(87)90076-5 | display-authors = 3 }}</ref>

Different mutagens act on DNA differently. Powerful mutagens may result in chromosomal instability,<ref>{{cite journal | vauthors = Huang L, Snyder AR, Morgan WF | title = Radiation-induced genomic instability and its implications for radiation carcinogenesis | journal = Oncogene | volume = 22 | issue = 37 | pages = 5848–54 | date = September 2003 | pmid = 12947391 | doi = 10.1038/sj.onc.1206697 | doi-access = free }}</ref> causing chromosomal breakages and rearrangement of the chromosomes such as [[Chromosomal translocation|translocation]], [[Deletion (genetics)|deletion]], and [[Chromosomal inversion|inversion]]. Such mutagens are called [[clastogen]]s.

Mutagens may also modify the DNA sequence; the changes in [[nucleic acid]] sequences by mutations include substitution of [[nucleotide]] [[base-pair]]s and [[insertional mutation|insertions]] and [[deletion (genetics)|deletions]] of one or more nucleotides in DNA sequences. Although some of these mutations are lethal or cause serious disease, many have minor effects as they do not result in residue changes that have significant effect on the structure and function of the [[protein]]s. Many mutations are [[silent mutation]]s, causing no visible effects at all, either because they occur in non-coding or non-functional sequences, or they do not change the [[amino-acid]] sequence due to the [[redundancy (information theory)|redundancy]] of [[codon]]s.<ref>{{cite journal |last1=Durland |first1=Justin |last2=Ahmadian-Moghadam |first2=Hamid |date=19 September 2022 |title=Genetics, Mutagenesis |url=https://www.ncbi.nlm.nih.gov/books/NBK560519/ |journal=StatPearls |volume=2023 Jan |doi= |access-date=18 November 2023}}
</ref>
Some mutagens can cause [[aneuploidy]] and change the number of chromosomes in the cell. They are known as aneuploidogens.<ref>{{cite journal | vauthors = Duesberg P, Rasnick D | title = Aneuploidy, the somatic mutation that makes cancer a species of its own | journal = Cell Motility and the Cytoskeleton | volume = 47 | issue = 2 | pages = 81–107 | date = October 2000 | pmid = 11013390 | doi = 10.1002/1097-0169(200010)47:2<81::AID-CM1>3.0.CO;2-# }}</ref>

In Ames test, where the varying concentrations of the chemical are used in the test, the dose response curve obtained is nearly always linear, suggesting that there may be no threshold for mutagenesis. Similar results are also obtained in studies with radiations, indicating that there may be [[Linear no-threshold model|no safe threshold]] for mutagens. However, the no-threshold model is disputed with some arguing for a [[threshold model|dose rate dependent threshold]] for mutagenesis.<ref>{{Cite web|url=https://phys.org/news/2017-01-calabrese-lnt-toxicology.html|title=Calabrese says mistake led to adopting the LNT model in toxicology|date=2017|website=phys.org|archive-url=https://web.archive.org/web/20170801234403/https://phys.org/news/2017-01-calabrese-lnt-toxicology.html|archive-date=1 August 2017|url-status=live|access-date=24 Jan 2019|postscript=. Calabrese says mistake led to adopting the LNT model in toxicology.}}</ref><ref name="Calabrese Nobel lecture"/> Some have proposed that low level of some mutagens may stimulate the [[DNA repair]] processes and therefore may not necessarily be harmful. More recent approaches with sensitive analytical methods have shown that there may be non-linear or bilinear dose-responses for genotoxic effects, and that the activation of DNA repair pathways can prevent the occurrence of mutation arising from a low dose of mutagen.<ref>{{cite journal | vauthors = Klapacz J, Pottenger LH, Engelward BP, Heinen CD, Johnson GE, Clewell RA, Carmichael PL, Adeleye Y, Andersen ME | title = Contributions of DNA repair and damage response pathways to the non-linear genotoxic responses of alkylating agents | journal = Mutation Research/Reviews in Mutation Research | volume = 767 | pages = 77–91 | date = 2016 | pmid = 27036068 | pmc = 4818947 | doi = 10.1016/j.mrrev.2015.11.001 | bibcode = 2016MRRMR.767...77K | display-authors = 3 }}</ref>

==Types of Mutagens==
Mutagens may be of physical, chemical or biological origin. They may act directly on the DNA, causing direct damage to the DNA, and most often result in replication error. Some however may act on the replication mechanism and chromosomal partition. Many mutagens are not mutagenic by themselves, but can form mutagenic metabolites through cellular processes, for example through the activity of the [[cytochrome P450]] system and other [[oxygenase]]s such as [[cyclooxygenase]].<ref>{{cite journal | vauthors = Kim D, Guengerich FP | title = Cytochrome P450 activation of arylamines and heterocyclic amines | journal = Annual Review of Pharmacology and Toxicology | volume = 45 | pages = 27–49 | date = 2005 | pmid = 15822170 | doi = 10.1146/annurev.pharmtox.45.120403.100010 }}</ref> Such mutagens are called [[promutagens]].{{fact|date=January 2025}}

===Physical mutagens===
* [[Ionizing radiation]]s such as [[X-rays]], [[gamma ray]]s and [[alpha particle]]s cause DNA breakage and other damages. The most common lab sources include [[cobalt-60]] and [[cesium-137]].
* [[Ultraviolet]] radiations with wavelength above 260&nbsp;nm are absorbed strongly by bases, producing [[pyrimidine dimers]], which can cause error in replication if left uncorrected.
* [[Radioactive decay]], such as [[Carbon-14|<sup>14</sup>C]] in DNA which decays into [[nitrogen]].

===Chemical mutagens===
[[Image:Benzopyrene DNA adduct 1JDG.png|thumb |right |200px |A [[DNA adduct]] (at center) of the mutagenic [[(+)-Benzo(a)pyrene-7,8-dihydrodiol-9,10-epoxide|metabolite]] of [[Benzo(a)pyrene|benzo[''a'']pyrene]] from [[tobacco smoking|tobacco smoke]]]]
Chemical mutagens either directly or indirectly damage DNA. On this basis, they are of 2 types:

====Directly acting chemical mutagens====
They directly damage DNA, but may or may not undergo metabolism to produce promutagens (metabolites that can have higher mutagenic potential than their substrates).
* [[Reactive oxygen species]] (ROS) – These may be [[superoxide]], [[hydroxyl radicals]] and [[hydrogen peroxide]], and large number of these highly reactive species are generated by normal cellular processes, for example as a by-products of mitochondrial [[Electron transport chain|electron transport]], or [[lipid peroxidation]]. As an example of the latter, 15-hydroperoxyeicosatetraenoic acid, a natural product of cellular cyclooxygenases and lipoxygenases, breaks down to form 4-hydroxy-2(''E'')-nonenal, 4-hydroperoxy-2(''E'')-nonenal, 4-oxo-2(''E'')-nonenal, and ''cis''-4,5-epoxy-2(''E'')-decanal; these bifunctional electophils are mutagenic in mammalian cells and may contribute to the development and/or progression of human cancers (see [[15-Hydroxyicosatetraenoic acid]]).<ref>{{cite journal | vauthors = Lee SH, Williams MV, Dubois RN, Blair IA | title = Cyclooxygenase-2-mediated DNA damage | journal = The Journal of Biological Chemistry | volume = 280 | issue = 31 | pages = 28337–46 | date = August 2005 | pmid = 15964853 | doi = 10.1074/jbc.M504178200 | display-authors = 3 | doi-access = free }}</ref> A number of mutagens may also generate these ROS. These ROS may result in the production of many base adducts, as well as DNA strand breaks and crosslinks.
* [[Deamination|Deaminating]] agents, for example [[nitrous acid]] which can cause transition mutations by converting [[cytosine]] to [[uracil]].
* [[Polycyclic aromatic hydrocarbon]]s (PAH), when activated to diol-epoxides can bind to DNA and form adducts.
* [[Alkylation|Alkylating]] agents such as [[ethylnitrosourea]]. The compounds transfer methyl or ethyl group to bases or the backbone phosphate groups. Guanine when alkylated may be mispaired with thymine. Some may cause DNA crosslinking and breakages. [[Nitrosamine]]s are an important group of mutagens found in tobacco, and may also be formed in smoked meats and fish via the interaction of amines in food with nitrites added as preservatives. Other alkylating agents include [[Sulfur mustard|mustard gas]] and [[vinyl chloride]].
* [[Aromatic amines]] and amides have been associated with carcinogenesis since 1895 when German physician [[Ludwig Rehn]] observed high incidence of bladder cancer among workers in German synthetic aromatic amine dye industry. [[2-Acetylaminofluorene]], originally used as a pesticide but may also be found in cooked meat, may cause cancer of the bladder, liver, ear, intestine, thyroid and breast.
* [[Alkaloid]] from plants, such as those from [[Vinca]] species,<ref>{{cite book |doi=10.1016/S0378-6080(05)80467-2 |chapter=Cytostatic drugs |title=Side Effects of Drugs Annual 28 |date=2005 |last1=Lipp |first1=Hans-Peter |last2=Hartmann |first2=Jörg Thomas |last3=Stanley |first3=Andrew |volume=28 |pages=538–551 |isbn=978-0-444-51571-1 }}</ref> may be converted by metabolic processes into the active mutagen or carcinogen.
* [[Bromine]] and some compounds that contain bromine in their chemical structure.<ref>{{cite journal | vauthors = Henderson JP, Byun J, Williams MV, Mueller DM, McCormick ML, Heinecke JW | title = Production of brominating intermediates by myeloperoxidase. A transhalogenation pathway for generating mutagenic nucleobases during inflammation | journal = The Journal of Biological Chemistry | volume = 276 | issue = 11 | pages = 7867–75 | date = March 2001 | pmid = 11096071 | doi = 10.1074/jbc.M005379200 | display-authors = 3 | doi-access = free }}</ref>
* [[Sodium azide]], an [[azide]] salt that is a common reagent in organic synthesis and a component in many car airbag systems
* [[Psoralen]] combined with ultraviolet radiation causes DNA cross-linking and hence chromosome breakage.
* [[Benzene]], an industrial solvent and precursor in the production of drugs, plastics, [[synthetic rubber]] and dyes.
* [[Chromium trioxide]], a highly toxic and oxidizing substance used in electroplating.<ref>{{cite journal | last1=Mamyrbaev | first1=Arstan Abdramanovich | last2=Dzharkenov | first2=Timur Agataevich | last3=Imangazina | first3=Zina Amangalievna | last4=Satybaldieva | first4=Umit Abulkhairovna | title=Mutagenic and carcinogenic actions of chromium and its compounds | journal=Environmental Health and Preventive Medicine | publisher=Springer Science and Business Media LLC | volume=20 | issue=3 | date=2015-04-16 | issn=1342-078X | doi=10.1007/s12199-015-0458-2 | pages=159–167| pmid=25877777 | pmc=4434237| bibcode=2015EHPM...20..159M }}</ref>

====Indirectly acting chemical mutagens====
They are not necessarily mutagenic by themselves, but they produce promutagens mutagenic compounds through metabolic processes in cells.
*[[Polyaromatic hydrocarbon]]s (PAHs)<ref>{{Cite journal |last=Yu |first=Hongtao |date=November 2002 |title=Environmental carcinogenic polycyclic aromatic hydrocarbons: photochemistry and phototoxicity |journal=Journal of Environmental Science and Health. Part C, Environmental Carcinogenesis & Ecotoxicology Reviews |volume=20 |issue=2 |pages=149–183 |doi=10.1081/GNC-120016203 |issn=1059-0501 |pmc=3812823 |pmid=12515673|bibcode=2002JESHC..20..149Y }}</ref>
*[[Aromatic amine]]s<ref>{{Cite book |last1=Cooke |first1=M. |last2=Dennis |first2=A. J. |date=1986-01-01 |title=Polynuclear aromatic hydrocarbons: Chemistry, characterization and carcinogenesis |osti=7252502 |url=https://www.osti.gov/biblio/7252502}}</ref>
*[[Benzene]]<ref>{{Cite journal |last1=Nishikawa |first1=Takuro |last2=Miyahara |first2=Emiko |last3=Horiuchi |first3=Masahisa |last4=Izumo |first4=Kimiko |last5=Okamoto |first5=Yasuhiro |last6=Kawai |first6=Yoshichika |last7=Kawano |first7=Yoshifumi |last8=Takeuchi |first8=Toru |date=January 2012 |title=Benzene metabolite 1,2,4-benzenetriol induces halogenated DNA and tyrosines representing halogenative stress in the HL-60 human myeloid cell line |journal=Environmental Health Perspectives |volume=120 |issue=1 |pages=62–67 |doi=10.1289/ehp.1103437 |issn=1552-9924 |pmc=3261936 |pmid=21859636|bibcode=2012EnvHP.120...62N }}</ref>

Some chemical mutagens additionally require [[UV light|UV]] or [[visible light]] activation for their mutagenic effect.  These are the {{vanchor|photomutagens|Photomutagen}}, which include [[furocoumarin]]s and [[limettin]].<ref>{{cite journal|last1=Raquet|first1=N|last2=Schrenk|first2=D|title=Relative photomutagenicity of furocoumarins and limettin in the hypoxanthine phosphoribosyl transferase assay in V79 cells.|journal=Chemical Research in Toxicology|date=September 2009|volume=22|issue=9|pages=1639–47|pmid=19725558|doi=10.1021/tx9002287}}</ref>

===Base analogs===
* [[Base analog]], which can substitute for DNA bases during replication and cause transition mutations. Some examples are [[5-Bromouracil|5-bromouracil]] and [[2-Aminopurine|2-aminopurine]].

===Intercalating agents===
* [[Intercalation (biochemistry)|Intercalating agents]], such as [[ethidium bromide]] and [[proflavine]], are molecules that may insert between bases in DNA, causing [[frameshift mutation]] during replication. Some such as [[daunorubicin]] may block transcription and replication, making them highly toxic to proliferating cells.{{citation needed|date=July 2022}}

===Metals===
Many metals, such as [[arsenic]], [[cadmium]], [[chromium]], [[nickel]] and their compounds may be mutagenic, but they may act, however, via a number of different mechanisms.<ref>{{cite journal |last1=Valko |first1=M. |last2=Morris |first2=H. |last3=Cronin |first3=M. |title=Metals, Toxicity and Oxidative Stress |journal=Current Medicinal Chemistry |date=May 2005 |volume=12 |issue=10 |pages=1161–1208 |doi=10.2174/0929867053764635 |pmid=15892631 }}</ref> Arsenic, chromium, iron, and nickel may be associated with the production of ROS, and some of these may also alter the fidelity of DNA replication. Nickel may also be linked to DNA hypermethylation and [[histone]] deacetylation, while some metals such as [[cobalt]], arsenic, nickel and cadmium may also affect DNA repair processes such as [[DNA mismatch repair]], and [[Base excision repair|base]] and [[nucleotide excision repair]].<ref>{{cite web|url=http://www.ebrc.de/industrial-chemicals-reach/projects-and-references/downloads/HERAG_FS_05_August_07.pdf|title=Health Risk Assessment Guidance for Metals – Mutagenicity|date=2007|work=EBRC|archive-url=https://web.archive.org/web/20120412230532/http://www.ebrc.de/industrial-chemicals-reach/projects-and-references/downloads/HERAG_FS_05_August_07.pdf|archive-date=12 April 2012}}</ref>

===Biological agents===
* [[Transposon]]s, a section of DNA that undergoes autonomous fragment relocation/multiplication. Its insertion into chromosomal DNA disrupts functional elements of the genes.
* [[Oncovirus]]es – Virus DNA may be inserted into the genome and disrupts genetic function. Infectious agents have been suggested to cause cancer as early as 1908 by Vilhelm Ellermann and Oluf Bang,<ref>{{cite journal |author1=Ellermann V. |author2=Bang O. |title=Experimentelle Leukämie bei Hühnern |journal=Zentralbl. Bakteriol. Parasitenkd. Infectionskr. Hyg. Abt. Orig. |year=1908 |volume=46 |pages=595–609 }}</ref> and 1911 by [[Peyton Rous]] who discovered the [[Rous sarcoma virus]].<ref>{{cite journal | vauthors = Rous P | journal = The Journal of Experimental Medicine | volume = 13 | issue = 4 | pages = 397–411 | date = April 1911 | pmid = 19867421 | pmc = 2124874 | doi = 10.1084/jem.13.4.397 | title = A Sarcoma of the Fowl Transmissible by an Agent Separable from the Tumor Cells }}</ref>
* [[Bacteria]] – some bacteria such as ''[[Helicobacter pylori]]'' cause inflammation during which oxidative species are produced, causing DNA damage and reducing efficiency of DNA repair systems, thereby increasing mutation.

==Protection==
[[File:Fruits veggies.png|thumb|right|Fruits and vegetables are rich in antioxidants.]]{{Main|Antimutagen|Antioxidants}}
[[Antioxidant]]s are an important group of [[anticarcinogenic]] compounds that may help remove [[Reactive oxygen species|ROS]] or potentially harmful chemicals. These may be found naturally in [[fruit]]s and [[vegetable]]s.<ref name="carcinogens and anticarcinogens">{{cite book|title=Carcinogens and Anticarcinogens in the Human Diet|last=National Research Council, U.S.|author-link=National Academies of Sciences, Engineering, and Medicine#Program units|publisher=National Academy Press|year=1996|isbn=978-0-309-05391-4|location=Washington, D.C.}}</ref> Examples of antioxidants are [[vitamin A]] and its [[carotenoid]] precursors, [[vitamin C]], [[vitamin E]], [[polyphenol]]s, and various other compounds. [[beta-Carotene|β-Carotene]] is the red-orange colored compounds found in vegetables like [[carrot]]s and [[tomato]]es. Vitamin C may prevent some cancers by inhibiting the formation of mutagenic [[N-nitroso]] compounds (nitrosamine). [[Flavonoid]]s, such as [[Epigallocatechin gallate|EGCG]] in [[green tea]], have also been shown to be effective antioxidants and may have anti-cancer properties. Epidemiological studies indicate that a diet rich in fruits and vegetables is associated with lower incidence of some cancers and longer life expectancy,<ref name="pmid22684632"/> however, the effectiveness of antioxidant supplements in cancer prevention in general is still the subject of some debate.<ref name="pmid22684632">{{cite journal | vauthors = Dolara P, Bigagli E, Collins A | title = Antioxidant vitamins and mineral supplementation, life span expansion and cancer incidence: a critical commentary | journal = European Journal of Nutrition | volume = 51 | issue = 7 | pages = 769–81 | date = October 2012 | pmid = 22684632 | doi = 10.1007/s00394-012-0389-2 | s2cid = 36973911 }}</ref><ref>{{cite journal | vauthors = Li K, Kaaks R, Linseisen J, Rohrmann S | title = Vitamin/mineral supplementation and cancer, cardiovascular, and all-cause mortality in a German prospective cohort (EPIC-Heidelberg) | journal = European Journal of Nutrition | volume = 51 | issue = 4 | pages = 407–13 | date = June 2012 | pmid = 21779961 | doi = 10.1007/s00394-011-0224-1 | s2cid = 1692747 | url = http://doc.rero.ch/record/313647/files/394_2011_Article_224.pdf | display-authors = 3 }}</ref>

Other chemicals may reduce mutagenesis or prevent cancer via other mechanisms, although for some the precise mechanism for their protective property may not be certain. [[Selenium]], which is present as a micronutrient in vegetables, is a component of important antioxidant enzymes such as gluthathione peroxidase. Many phytonutrients may counter the effect of mutagens; for example, [[sulforaphane]] in vegetables such as [[broccoli]] has been shown to be protective against [[prostate cancer]].<ref>{{cite journal | vauthors = Gibbs A, Schwartzman J, Deng V, Alumkal J | title = Sulforaphane destabilizes the androgen receptor in prostate cancer cells by inactivating histone deacetylase 6 | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 106 | issue = 39 | pages = 16663–8 | date = September 2009 | pmid = 19805354 | pmc = 2757849 | doi = 10.1073/pnas.0908908106 | bibcode = 2009PNAS..10616663G | display-authors = 3 | doi-access = free }}</ref> Others that may be effective against cancer include [[indole-3-carbinol]] from [[cruciferous vegetables]] and [[resveratrol]] from red wine.<ref>{{cite journal | vauthors = Gullett NP, Ruhul Amin AR, Bayraktar S, Pezzuto JM, Shin DM, Khuri FR, Aggarwal BB, Surh YJ, Kucuk O | title = Cancer prevention with natural compounds | journal = Seminars in Oncology | volume = 37 | issue = 3 | pages = 258–81 | date = June 2010 | pmid = 20709209 | doi = 10.1053/j.seminoncol.2010.06.014 | display-authors = 3 }}</ref>

An effective precautionary measure an individual can undertake to protect themselves is by limiting exposure to mutagens such as UV radiations and tobacco smoke. In Australia, where people with pale skin are often exposed to strong sunlight, [[melanoma]] is the most common cancer diagnosed in people aged 15–44 years.<ref>{{cite web|url=http://www.cancer.org.au/cancersmartlifestyle/SunSmart/Skincancerfactsandfigures.htm|title=Skin Cancer Facts and Figures|website=Cancer Council|archive-url=https://web.archive.org/web/20120810071104/http://www.cancer.org.au/cancersmartlifestyle/SunSmart/Skincancerfactsandfigures.htm|archive-date=10 August 2012|access-date=2 Jul 2010}}</ref><ref>{{Cite news|url=https://www.newscientist.com/article/dn13922-skin-tone-gene-could-predict-cancer-risk/|title=Skin-tone gene could predict cancer risk|last=Callaway|first=E|date=2008|work=New Scientist|access-date=24 Jan 2019|archive-url=https://web.archive.org/web/20150424063714/http://www.newscientist.com/article/dn13922-skintone-gene-could-predict-cancer-risk.html|archive-date=24 April 2015|url-status=live}}</ref>

In 1981, human epidemiological analysis by [[Richard Doll]] and [[Richard Peto]] indicated that smoking caused 30% of cancers in the US.<ref>{{cite journal | vauthors = Doll R, Peto R | title = The causes of cancer: quantitative estimates of avoidable risks of cancer in the United States today | journal = Journal of the National Cancer Institute | volume = 66 | issue = 6 | pages = 1191–308 | date = June 1981 | pmid = 7017215 | doi = 10.1093/jnci/66.6.1192 }}</ref> Diet is also thought to cause a significant number of cancer fatalities, and it has been estimated that around 32% of cancer deaths may be avoidable by modification to the diet.<ref>{{cite journal | vauthors = Willett WC | title = Diet, nutrition, and avoidable cancer | journal = Environmental Health Perspectives | volume = 103 | issue = Suppl 8 | pages = 165–70 | date = November 1995 | pmid = 8741778 | pmc = 1518978 | doi = 10.1289/ehp.95103s8165 | bibcode = 1995EnvHP.103S.165W }}</ref> Mutagens identified in food include [[mycotoxin]]s from food contaminated with fungal growths, such as [[aflatoxins]] which may be present in contaminated peanuts and corn; [[heterocyclic amine]]s generated in meat when cooked at high temperature; PAHs in charred meat and smoked fish, as well as in oils, fats, bread, and cereal;<ref name="PAH in diet">{{cite web|url=http://ec.europa.eu/food/fs/sc/scf/out154_en.pdf|title=Polycyclic Aromatic Hydrocarbons – Occurrence in foods, dietary exposure and health effects|author=Scientific Committee on Food|date=4 Dec 2002|publisher=[[European Commission]]|archive-url=https://web.archive.org/web/20110519225348/http://ec.europa.eu/food/fs/sc/scf/out154_en.pdf|archive-date=19 May 2011|access-date=21 Aug 2010}}</ref> and nitrosamines generated from nitrites used as food preservatives in [[cured meat]] such as [[bacon]] ([[Vitamin C|ascorbate]], which is added to cured meat, however, reduces nitrosamine formation).<ref name="carcinogens and anticarcinogens"/> Overly-browned starchy food such as bread, biscuits and potatoes can generate [[acrylamide]], a chemical shown to cause cancer in animal studies.<ref>{{cite news|url=https://www.theguardian.com/world/2017/jan/23/toast-thats-a-bit-too-brown-may-cause-cancer-say-authorities|title=Roast potatoes and toast that's a bit too brown may cause cancer, say authorities|last=Siddique|first=Haroon|date=23 Jan 2017|work=[[The Guardian]]|archive-url=https://web.archive.org/web/20170123142506/https://www.theguardian.com/world/2017/jan/23/toast-thats-a-bit-too-brown-may-cause-cancer-say-authorities|archive-date=23 January 2017|url-status=live}}</ref><ref>{{cite journal | vauthors = Tareke E, Rydberg P, Karlsson P, Eriksson S, Törnqvist M | title = Analysis of acrylamide, a carcinogen formed in heated foodstuffs | journal = Journal of Agricultural and Food Chemistry | volume = 50 | issue = 17 | pages = 4998–5006 | date = August 2002 | pmid = 12166997 | doi = 10.1021/jf020302f | bibcode = 2002JAFC...50.4998T }}</ref> Excessive [[Alcohol and cancer|alcohol consumption]] has also been linked to cancer; the possible mechanisms for its carcinogenicity include formation of the possible mutagen [[acetaldehyde]], and the induction of the [[cytochrome P450]] system which is known to produce mutagenic compounds from promutagens.<ref>{{cite journal | vauthors = Pöschl G, Seitz HK | title = Alcohol and cancer | journal = Alcohol and Alcoholism | volume = 39 | issue = 3 | pages = 155–65 | year = 2004 | pmid = 15082451 | doi = 10.1093/alcalc/agh057 | url = https://academic.oup.com/alcalc/article-pdf/39/3/155/470412/agh057.pdf }}</ref>

For certain mutagens, such as dangerous chemicals and radioactive materials, as well as infectious agents known to cause cancer, government legislations and regulatory bodies are necessary for their control.<ref>{{Cite book|title=Genetics and the Law II|vauthors=Milunsky A, Annas GJ|publisher=Springer US|year=1980|isbn=978-1-4613-3080-6|location=Boston, MA}}</ref>

==Test systems==
Many different systems for detecting mutagen have been developed.<ref>{{cite book |doi=10.1002/0471646776.ch21 |chapter=Toxicity Testing |title=A Textbook of Modern Toxicology |date=2004 |last1=Cunny |first1=Helen |last2=Hodgson |first2=Ernest |pages=351–397 |isbn=978-0-471-26508-5 }}</ref><ref>{{cite book|title=Principles of Toxicology – Environmental and Industrial Applications|last1=Williams|first1=Phillip L.|last2=James|first2=Robert C.|last3=Roberts|first3=Stephen M.|publisher=John Wiley & Sons|year=2000|isbn=978-0-471-29321-7|edition=2nd|name-list-style=vanc}}</ref> Animal systems may more accurately reflect the metabolism of human, however, they are expensive and time-consuming (may take around three years to complete), they are therefore not used as a first screen for mutagenicity or carcinogenicity.

=== Bacterial ===
{{main|Ames test}}
* '''Ames test''' – This is the most commonly used test, and ''[[Salmonella typhimurium]]'' strains deficient in [[histidine]] biosynthesis are used in this test. The test checks for mutants that can revert to wild-type. It is an easy, inexpensive and convenient initial screen for mutagens.
* '''Resistance to 8-azaguanine in ''S. typhimurium''''' – Similar to Ames test, but instead of reverse mutation, it checks for forward mutation that confer resistance to [[8-Azaguanine]] in a histidine revertant strain.
* '''''Escherichia coli'' systems''' – Both forward and reverse mutation detection system have been modified for use in ''[[Escherichia coli|E. coli]]''. [[Tryptophan]]-deficient mutant is used for the reverse mutation, while galactose utility or resistance to 5-methyltryptophan may be used for forward mutation.
* '''DNA repair''' – ''E. coli'' and ''[[Bacillus subtilis]]'' strains deficient in DNA repair may be used to detect mutagens by their effect on the growth of these cells through DNA damage.

=== Yeast ===
Systems similar to Ames test have been developed in yeast. ''[[Saccharomyces cerevisiae]]'' is generally used. These systems can check for forward and reverse mutations, as well as recombinant events.

=== ''Drosophila'' ===
'''[[Sex linkage|Sex-Linked]] Recessive Lethal Test''' – Males from a strain with yellow bodies are used in this test. The gene for the yellow body lies on the X-chromosome. The fruit flies are fed on a diet of test chemical, and progenies are separated by sex. The surviving males are crossed with the females of the same generation, and if no males with yellow bodies are detected in the second generation, it would indicate a lethal mutation on the X-chromosome has occurred.

===Plant assays===
Plants such as ''[[Zea mays]]'', ''[[Arabidopsis thaliana]]'' and ''[[Tradescantia]]'' have been used in various test assays for mutagenecity of chemicals.

===Cell culture assay===
Mammalian cell lines such as Chinese hamster V79 cells, [[Chinese hamster ovary cell|Chinese hamster ovary]] (CHO) cells or mouse lymphoma cells may be used to test for mutagenesis. Such systems include the '''[[Hypoxanthine-guanine phosphoribosyltransferase|HPRT]] assay''' for resistance to 8-azaguanine or [[6-thioguanine]], and '''[[ouabain]]-resistance (OUA) assay'''.

Rat primary hepatocytes may also be used to measure DNA repair following DNA damage. Mutagens may stimulate unscheduled DNA synthesis that results in more stained nuclear material in cells following exposure to mutagens.

===Chromosome check systems===
These systems check for large scale changes to the chromosomes and may be used with cell culture or in animal test. The chromosomes are stained and observed for any changes. '''Sister chromatid exchange''' is a symmetrical exchange of chromosome material between sister chromatids and may be correlated to the mutagenic or carcinogenic potential of a chemical. In '''micronucleus Test''', cells are examined for micronuclei, which are fragments or chromosomes left behind at anaphase, and is therefore a test for clastogenic agents that cause chromosome breakages. Other tests may check for various chromosomal aberrations such as chromatid and chromosomal gaps and deletions, translocations, and ploidy.

===Animal test systems===
[[Rodents]] are usually used in [[Animal testing on rodents|animal test]]. The chemicals under
test are usually administered in the food and in the drinking water, but sometimes by dermal application, by [[Feeding tube|gavage]], or by inhalation, and carried out over the major part of the life span for rodents. In tests that check for carcinogens, maximum tolerated dosage is first determined, then a range of doses are given to around 50 animals throughout the notional lifespan of the animal of two years. After death the animals are examined for sign of tumours. Differences in metabolism between rat and human however means that human may not respond in exactly the same way to mutagen, and dosages that produce tumours on the animal test may also be unreasonably high for a human, i.e. the equivalent amount required to produce tumours in human may far exceed what a person might encounter in real life.

Mice with recessive mutations for a visible phenotype may also be used to check for mutagens. Females with recessive mutation crossed with wild-type males would yield the same phenotype as the wild-type, and any observable change to the phenotype would indicate that a mutation induced by the mutagen has occurred.

Mice may also be used for '''dominant lethal assays''' where early embryonic deaths are monitored. Male mice are treated with chemicals under test, mated with females, and the females are then sacrificed before parturition and early fetal deaths are counted in the [[uterine horns]].

'''[[Genetically modified mouse|Transgenic mouse]] assay''' using a mouse strain infected with a viral [[shuttle vector]] is another method for testing mutagens. Animals are first treated with suspected mutagen, the mouse DNA is then isolated and the phage segment recovered and used to infect ''E. coli''. Using similar method as the [[blue-white screen]], the plaque formed with DNA containing mutation are white, while those without are blue.

== In anti-cancer therapy ==
Many mutagens are highly toxic to proliferating cells, and they are often used to destroy cancer cells. Alkylating agents such as [[cyclophosphamide]] and [[cisplatin]], as well as intercalating agent such as [[daunorubicin]] and [[doxorubicin]] may be used in [[chemotherapy]]. However, due to their effect on other cells which are also rapidly dividing, they may have side effects such as hair loss and nausea. Research on better targeted therapies may reduce such side-effects. Ionizing radiations are used in [[radiation therapy]].

== In fiction ==
In [[science fiction]], mutagens are often represented as substances that are capable of completely changing the form of the recipient or granting them superpowers. Powerful radiations are the agents of mutation for the [[superheroes]] in [[Marvel Comics]]'s [[Fantastic Four]], [[Daredevil (Marvel Comics series)|Daredevil]], and [[Hulk]], while in the [[Ninja Turtles]] franchise the MUTAGEN  "ooze" for [[Inhumans]] the mutagen is the [[Terrigen Mist]]. Mutagens are also featured in video games such as ''[[Cyberia (video game)|Cyberia]],'' [[System Shock]], ''[[The Witcher (video game)|The Witcher]]'', ''[[Metroid Prime: Trilogy]]'', ''[[Resistance: Fall of Man]]'', ''[[Resident Evil]]'', ''[[Infamous (video game)|Infamous]]'',  ''[[Freedom Force (2002 video game)|Freedom Force]], [[Command & Conquer]]'', ''[[Gears of War 3]]'', ''[[StarCraft]]'', ''[[BioShock]]'', ''[[Fallout (video game)|Fallout]]'', ''[[Underrail]]'', and ''[[Maneater (video game)|Maneater]]''.
In the "nuclear monster" films of the 1950s, nuclear radiation mutates humans and common insects often to enormous size and aggression; these films include ''[[Godzilla (1954 film)|Godzilla]]'', ''[[Them!]]'', ''[[Attack of the 50 Foot Woman]]'', ''[[Tarantula!]]'', and ''[[The Amazing Colossal Man]]''.

==See also==
* [[Carcinogenesis]]
* [[DNA damage (naturally occurring)]]
* [[Linear no-threshold model]]

== References ==
{{Reflist|30em}}

{{Toxicology}}
{{Genotoxicity}}

[[Category:Mutagens| ]]
[[Category:Mutation]]
[[Category:Radiation health effects]]
[[Category:Radioactivity]]

[[it:Mutazione genetica#Mutazioni indotte]]