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In [[biology]], a '''mutagen''' ([[Latin]], literally ''origin of change'') is a physical or chemical agent that changes the genetic information (usually [[DNA]]) of an [[organism]] and thus increases the frequency of [[mutation]]s above the natural background level. As many mutations cause [[cancer]], mutagens are typically also [[carcinogen]]s. Not all [[mutations]] are caused by mutagens: So-called "spontaneous mutations" occur due to errors in [[DNA replication]], repair and recombination of [[DNA sequences]].

==Effects of mutations==

The changes in nucleic acid sequences by mutations include substitution of [[nucleotide]] [[base-pair]]s and insertions and deletions of one or more nucleotides in DNA sequences. Although many of these mutations are lethal, or cause serious disease, some have minor effects, as the changes they cause in the sequence of encoded proteins are not significant. Many mutations cause no visible effects at all, either because they occur in [[intron]]s, or because they do not change the amino-acid sequence, due to [[Redundancy (information theory)|redundancy]] of [[codon]]s.

==Genetic drift==

The change in a population’s genetic material due to the accumulation of random chance is called drift and serves as a [[molecular clock]]. In general, the more nucleotide differences between two organisms, the more time has elapsed since their last common ancestor. Though it is difficult to determine in many organisms, estimates for mutation rates have been made for both ''[[E. coli]]'' and [[eukaryotes]].  It was estimated that in these organisms about one nucleotide in every 10<sup>10</sup> is changed and continues through reproduction to future generations of cells.

==Discovery of mutagenesis==

In the [[1920s]], [[Hermann Muller]] discovered that [[x-ray]]s caused mutations in fruit flies.  He went on to use x-rays to create [[Drosophila]] mutants that he used in his studies of [[genetics]].  He also discovered that x-rays did not only mutate genes in fruit flies, but also had effects on the genetic makeup of humans.<ref>Campbell, Neil A. and Jane B. Reece. Biology. 7th ed. San Francisco, CA: Pearson Education, Inc, 2005.</ref>

==Nature of mutagens==

Mutagens are usually [[chemical compound]]s or [[ionizing radiation]].  Mutagens can be divided into different categories according to their effect on DNA replication:

*Some mutagens act as base analogs and get inserted into the DNA strand during replication in place of the substrates.
*Some react with DNA and cause structural changes that lead to miscopying of the template strand when the DNA is replicated.
*Some work indirectly by causing the cells to synthesize chemicals that have the direct mutagenic effect.

The [[Ames test]] is one method to determine how mutagenic an agent is.

==Examples==
*[[Nitrous acid]], (HNO<sub>2</sub>) [[Deamination|Deaminating]] agent
*[[UV Radiation]], thymine dimer formation
*[[Sodium azide]],  (NaN<sub>3</sub>)
*[[Gamma radiation|Gamma]] and [[Alpha Radiation]], ionising radiations
* [[Transposons]], autonomous DNA fragment relocation/multiplication
* Base analogues, substitutes
* Bromine and some of its compounds,
* [[Ethidium bromide]] (EtBr), and other intercalating agents.
* Bromouracil,Alkylating Agent
* Vinca Alkaloids, Natural Plant Alkaloid

== Mutagens in fiction ==
In [[science fiction]], mutagens are often represented as substances that are capable of completely changing the form of the recipient. 

* The [[Inhumans (comics)|Inhumans]] of [[Marvel Comics]] utilize a mutagen called the "[[Terrigen Mist]]".
* The [[Teenage Mutant Ninja Turtles]] were supposedly created by means of mutagens, as well as their master [[Splinter (TMNT)|Splinter]] and (in the 1987 cartoon) their enemies [[Bebop and Rocksteady]].
* In the [[Street Fighter (film)|Street Fighter]] movie, a bag of mutagens is used by General Bison to transform Carlos Blanka into a monster.
* In [[Lego]]'s [[Bionicle]] franchise, the water surrounding the pit is mutagenic, causing mutation in most of the major characters who enter the water.

==References==
<references/>

== See also ==
* [[Carcinogen]]
* [[DNA repair]]
* [[Genetics]]
* [[Pesticide]]
* [[Teratogen]]

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

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