Mutagen: Types & Examples

Joanna Tatomir, April Koch
  • Author
    Joanna Tatomir

    Joanna holds a PhD in Biology from the University of Michigan and is currently working towards a degree in Veterinary Medicine at Michigan State University. She has taught a combination of ESL and STEM courses to secondary and university students.

  • Instructor
    April Koch

    April teaches high school science and holds a master's degree in education.

Learn what a mutagen is. Understand types of mutagens, explore how mutagens cause mutations, and see examples of how mutations affect the real world. Updated: 11/11/2021

Table of Contents


What is a Mutagen?

A mutagen refers to any agent found in an organism's environment capable of producing genetic mutations in DNA. Under normal circumstances, DNA replication occurs without the introduction of mutations or changes in the genetic code of an organism. This is due to the presence of DNA repair mechanisms such as base excision repair (BER), nucleotide excision repair (NER), and mismatch repair (MMR). In base excision repair, a damaged base is removed from the DNA during the G1 stage of the normal cell cycle. Nucleotide excision repair occurs during the G1 and G2 stages of the cell cycle and deletes lesions that form on nucleotide sequences in DNA. Even after the cell cycle is complete, mismatch repair can occur after replication to ensure that base pair matching is maintained within the DNA.

However, in some cases, mutations persist in the DNA due to the presence of mutagenic agents. What does mutagenic mean? The term mutagenic is defined as the ability to induce genetic changes in the DNA of an organism. There are many sources of mutagenic agents, including physical, chemical, and biological mechanisms. Some examples of physical mutagens include UV or gamma radiation while alkylating agents and azides represent potential chemical mutagens. Biological mutagens often consist of viruses and different bacterial species capable of initiating changes in an individual's DNA.

Examples of these different types of mutagens and their potential effects on the human body are explored as part of this lesson.

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  • 0:33 Mutation Formation
  • 2:01 Mutagens
  • 3:31 Mutations and DNA Polymerase
  • 3:59 Mutations in the Real World
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Types and Examples of Mutagens

Mutagens are often classified based on their origin and their effects upon DNA. There are three basic types of mutagens:

  • Physical mutagens
  • Chemical mutagens
  • Biological mutagens

Physical mutagens include ultraviolet and gamma radiation. Both sources induce the creation of free radicals or molecules having unpaired electrons. These free radicals can then cause unintentional bonds to form between bases, such as covalent bonds between thymine molecules. The creation of the thymine dimer prevents the double helix from forming wherever this dimer exists in the nucleotide sequence. The condition xeroderma pigmentosum, in which individuals have an increased risk of skin cancer due to extreme light sensitivity, is caused by the lack of an enzyme needed to remove thymine dimers from DNA sequences.

An example of DNA damage caused by UV radiation.

Mutagen examples

Chemical mutagens are commonly found in compounds that produce toxicity and concomitant damage to DNA. Alkylators, one type of chemical mutagen, directly impact bases by creating G (guanine) residues resulting in depurination or loss of a purine. This creates a mismatch between base pairs and induces DNA repair mechanisms to allow these mutations to persist in the DNA sequence. Other chemical mutagens like nitrous acid cause base switching in which cytosine is converted to uracil, adenine is changed to hypoxanthine, and guanine is transformed to xanthine. These altered bases still undergo base pairing, even though this often results in miscoded regions of DNA.

Examples of direct damage to bases in DNA.

Mutagen examples

Biological mutagens consist of bacteria and viruses capable of producing mutations in DNA. Human papillomavirus (HPV), for example, results in long-term infection in individuals unable to clear the virus from their bodies. Infected tissues are located in the cervix, throat, and other regions of the reproductive tract in men, while women undergo mutagenesis, in which precancerous cells develop in response to the virus.

Healthy cervical cells on the left and HPV infected cells on the right.

Mutagen examples

Some specific mutagen examples include:

Agent Mutagen Type  Effect 
UV radiation  Physical  Thymine dimers
Gamma radiation  Physical  Thymine dimers 
Ethyl methane sulfonate  Chemical  G residues, depurination and base mispairing 
Methyl methane sulfonate  Chemical  G residues, depurination and base mispairing 
Diethylsulfate  Chemical  G residues, depurination and base mispairing  
Nitrosoguanidine  Chemical  G residues, depurination and base mispairing  
Human papilloma virus  Biological Cancers of the reproductive and digestive tract
Epstein Barr virus  Biological  Lymphoma 
Hepatitis B, C viruses  Biological  Liver cancer 
Helicobacter pylori  Biological  Stomach cancer 
Chlamydia trachomatis  Biological   Cervical cancer

How a Mutagen Works

Mutagens create damage to DNA by disrupting the normal replication and genetic repair mechanisms. In healthy individuals under normal conditions, DNA is built by adding nucleotides to the 3' ends of DNA strands. There are at least fifteen different forms of DNA polymerase that facilitate this process by performing replication, repair, and proofreading of DNA. When exposed to a mutagen, errors in DNA replication occur. This results from the replacement of normal human DNA polymerase with Y-family polymerases that bypass DNA repair mechanisms. The main mutagenic effects produced by this switch include an increase in error-prone replication, creation of frameshift mutations, and prevention of genetic replication.

DNA repair mechanisms in response to the mutagenic effect.

Mutagenic effect

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Frequently Asked Questions

What is a mutagen in biology?

A mutagen refers to any agent capable of producing damage to DNA. This results in the formation of mutations, the primary source of genetic diversity in populations.

What are the three types of mutagens?

There are three main types of mutagens: physical, chemical, and biological. Each type results in damage to DNA during the processes of replication and repair.

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