What Causes Mutations? Piecing Together DNA's Puzzling Edits

By: Elizabeth Sprouse & Desiree Bowie  | 
Illustration of DNA chain with a mutation on one fragment.
Environmental influences and errors during cell replication are two factors that could be responsible for a genetic variation in DNA. Maciej Frolow / Getty Images

Think of your community's traffic. When the traffic lights are functioning, drivers (usually) behave. Break a light, and everything comes to a standstill. Within our bodies, we could liken that broken traffic light to a DNA mutation — one that has the potential to mess up our body's everyday operations. So where lightning might knock out a traffic light, what causes mutations in DNA?

In our bodies, a mutation refers to a change in the DNA sequence, which is the intricate order of genetic material. While there are mutations that can be disruptive or even harmful (akin to a broken traffic light), many are neutral and others can be incredibly beneficial.


Let's explore some of the common causes of mutations, which can include everything from external factors like UV radiation and viruses to internal errors during DNA replication.

What Is DNA?

DNA, or deoxyribonucleic acid, is a molecule that carries the genetic material crucial for the development, functioning and reproduction of all known living organisms.

Structurally, DNA is a long molecule comprised of units called nucleotides. Each nucleotide consists of a phosphate group, a deoxyribose sugar and one of four nitrogenous bases: adenine, thymine, cytosine or guanine.


When two DNA strands coil, they form the double helix, with adenine pairing with thymine, and cytosine with guanine. This specific structure ensures accurate replication during cell division.

Chromosomes and Mutations

In human cells, DNA is organized into chromosomes, typically having 23 pairs. Genes, specific segments within these chromosomes, guide the creation of proteins, the body's main functional units.

As cells divide and DNA replicates, errors might arise, leading to mutations. Some mutations, especially those in egg and sperm cells, can be passed to the next generation, potentially causing genetic disorders or diseases.

On the other hand, a somatic mutation affects only the individual and isn't inherited by subsequent generations.


What Causes Mutations?

Genes, or segments within our DNA, encode instructions for producing proteins vital to our survival. These proteins provide structure, function and regulation to our tissues and organs. Alterations to these instructions, via genetic mutations, might compromise essential proteins.

So what causes these mutations? Two things: errors during cell replication and environmental influences.


Our cells continuously replicate their DNA to replace old or damaged cells. During this process, the double-stranded DNA separates, and each strand is copied to form a new double strand.

Approximately once in every 100 million replications, an error happens, potentially leading to a genetic mutation. We can certainly take comfort in that statistic, as well as the fact that our DNA does a stand-up job of repairing itself when mutations occur.

Now let's look at the intrinsic and external factors that can change these DNA molecules.


Internal Factors

As we've mentioned, one of the primary sources of these mutations is errors that occur during DNA replication. Every time a cell divides, it must copy its entire DNA, and occasionally, it can misread or miss a piece, leading to mutations.

Tautomeric Shifts

In some cases, the structure of DNA building blocks can momentarily change, a phenomenon known as tautomeric shifts. If DNA is copied during one of these shifts, it can lead to incorrect pairings and subsequently mutations.


Natural chemical reactions in our cells — like the conversion of one DNA part, cytosine, to another called uracil — can also introduce errors if not corrected.


Then there's a process called slipped strand mis-pairing. Imagine DNA as a zipper: Sometimes, when "zipping," a tooth can misalign, especially in areas with repetitive patterns. This can cause parts of the DNA to be added or skipped.

Jumping Genes

And finally, our DNA contains movable elements known as transposons. These "jumping genes" can relocate within our DNA, and if they insert themselves into critical regions, they can disrupt the function, causing mutations.

Mutations caused by factors like transposons can result in the creation of a mutant allele, which is a variant form of a gene. Our cells work hard to fix these errors, but occasionally some slip through, potentially leading to health issues.


External Factors

Environmental factors play a significant role in inducing mutations. External physical agents, especially radiation, are powerful mutagens.


Ultraviolet (UV) radiation, for instance, induces the formation of pyrimidine dimers, notably thymine dimers, that distort the DNA structure.


Pyrimidine dimers are like "sunburns" on DNA. They happen when two DNA building blocks, usually caused by UV light from the sun, stick together incorrectly. This "sticking" can interfere with the normal function of DNA.

X-rays and gamma rays can cause single- and double-strand breaks in DNA, yielding mutations such as deletions, insertions or translocations. Basically, this damage can lead to missing pieces, extra pieces or shuffled parts in our DNA, causing changes called mutations.

Chemical Factors

Chemical agents introduce another dimension of external mutations. Some chemicals, known as base analogues, mimic nucleotides and can be mistakenly incorporated into DNA, leading to incorrect pairing in subsequent replication cycles.

Some chemicals, like 5-Bromouracil, can trick our DNA and cause errors. Others, known as alkylating agents, stick extra parts onto our DNA, which can lead to mistakes.

Deaminating agents remove specific parts from our DNA, while chemicals like ethidium bromide slide between our DNA pieces, causing them to shift and change order. Harmful substances in cigarette smoke, like benzo[a]pyrene, can stick to our DNA and change its shape.

Biological Factors

Lastly, biological agents, such as viruses, might integrate their DNA into a host's genome, leading to mutations.

Environmental Foes

Extreme temperatures might boost mutation rates, and some foods or lifestyle habits, like smoking, expose individuals to mutagenic chemicals. However, mutations can also be caused by environmental foes.

Tobacco, ultraviolet light and other chemicals are all potential enemies of DNA. One way these hazards attack our genes is very sneaky: They have the ability to damage the chemicals making up DNA. For example, the mutagens like to swap the chemicals out or disguise one for another. This becomes a big deal when our DNA starts replicating itself because those chemicals don't behave correctly.


DNA Repair: The Guardian of Our Genetic Code

Mutations can pop up when DNA is copied or exposed to harmful things like too much sunlight. Here's how our cells tackle these errors:

  1. Direct fix: Some errors are small, like tiny road cracks. The cell directly fixes them, almost like using a quick patch.
  2. Mismatch repair: After copying DNA, cells double-check their work. If they spot a mismatch, they correct it, ensuring the new DNA matches the original.
  3. Excision repair: For bigger damages, like those from sunburn, cells cut out the bad part and fill in with the right piece.
  4. Strand repair: If a section of DNA gets damaged, cells can use the other DNA strand as a backup to fix the mistakes.


The ABCs of Genetic Testing

Genetic testing is a process used to examine genes, chromosomes or proteins in our DNA. It starts with taking a sample, often from blood or saliva. This sample is processed to extract and purify the DNA, making it ready for analysis.

Scientists use various techniques to study this DNA:


  • Sequencing identifies the order of the DNA building blocks and finds any changes from what's expected.
  • The Polymerase Chain Reaction (PCR) makes many copies of specific DNA parts for closer examination.
  • Microarrays scan the DNA for known mutations, and gene panels focus on certain genes associated with specific conditions.

After analyzing the DNA, the results are compared to standard references to spot any differences or mutations. A report is then made that details any findings, including potential health risks or genetic conditions. This information can help understand inherited traits or risks for certain diseases.

This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.


Lots More Information

Related Articles

  • Learn. Genetics. Genetic Science Learning Center. "What Causes DNA Mutations?" May 28, 2010. (September 20, 2010) http://learn.genetics.utah.edu/archive/sloozeworm/mutationbg.html
  • TeensHealth. "The Basics on Genes and Genetic Disorders." April 2009. (September 20, 2010) http://kidshealth.org/teen/your_body/health_basics/genes_genetic_disorders.html
  • University of California Museum of Paleontology. "Understanding Evolution." (September 20, 2010) http://evolution.berkeley.edu/evolibrary/article/mutations_01
  • U.S. National Library of Medicine. "Handbook: Help Me Understand Genetics." July 25, 2010. (July 26, 2010)http://ghr.nlm.nih.gov/handbook