A gene mutation, which may also be called a gene variant, is a change in the structure of a gene, the unit of heredity. Genes are made of deoxyribonucleic acid (DNA), a long molecule composed of building blocks called nucleotides. Each nucleotide is built around one of four different subunits, called bases. These bases are known as guanine, cytosine, adenine and thymine. A gene carries information in the sequence of its nucleotides, just as a sentence carries information in the sequence of its letters.

Types of Mutations and Their Effects

One type of mutation is a change to a base. This is called a point mutation, and it is like changing one letter in a word. Genes carry instructions for making proteins. When a base is changed in a gene, different results are possible, depending on which base is changed and what it is changed into. The gene may produce an altered protein, it may produce no protein, or it may produce the usual protein. Most mutations are not harmful, but some can be. A harmful mutation can result in a genetic disorder or even cancer.

Another kind of mutation is a chromosomal mutation. Chromosomes, located in the cell nucleus, are tiny threadlike structures that carry genes. A chromosome consists of a molecule of DNA and proteins. Sometimes, a long segment of DNA is inserted into a chromosome, deleted from a chromosome, flipped around within a chromosome, duplicated, or moved from one chromosome to another in these mutations. Such changes are usually very harmful.

One example of a chromosomal mutation is a condition called Down syndrome. In humans, each cell typically has two copies of 23 chromosomes, for a total of 46 chromosomes. Down syndrome usually results from the presence of one extra copy of a particular chromosome, or an extra portion of that chromosome. The presence of that extra chromosome leads to problems with certain organs of the body, such as the heart. It can also lead to leukemia—a cancer of the blood-forming cells—and produce intellectual disabilities. Many people with Down syndrome also have distinct facial features.

Mutations, Inheritance and Evolution

Mutations can be inherited or acquired later in life. Mutations that an individual inherits from their parents are called hereditary mutations. They are present in all body cells and can be passed down to new generations. Acquired mutations occur during an individual’s life.

If a mutation occurs in an egg or sperm cell, it can be passed down to the individual’s offspring. Once a mutation is passed down, it is a hereditary mutation. Acquired mutations are not passed down if they occur in the somatic cells, which are body cells other than sperm cells and egg cells. Some acquired mutations occur spontaneously and randomly in genes. Other mutations are caused by environmental factors, such as exposure to certain chemicals or radiation.

Mutations occur throughout the natural world. Some mutations are beneficial and increase the possibility that an organism will thrive and, therefore, pass on its genes to the next generation. When mutations improve survival or reproduction, the process of natural selection causes the mutation to become more common over time. When mutations are harmful, they become less common over time. In this way, mutations help drive evolution.

Evolution is the process by which species and traits change over generations. Even before the modern understanding of genes and mutations came about, theories about evolution argued that changes in inherited traits were important factors in changing species. In the early 1800s, Jean-Baptiste Lamarck claimed that offspring inherit traits that their parents acquire from changing their own behaviors and bodies. The classic example that Lamarck gave was giraffes. He claimed that giraffes evolved long necks because giraffe ancestors would continually stretch their necks to reach for food. Lamarck believed that this happened until the giraffe neck reached its current length. But this idea failed to explain how traits were passed on and why some acquired traits are passed on and others are not.

In 1859, Charles Darwin proposed the theory of evolution in his book On the Origin of Species. This theory explains that among individuals of a species, variations in traits arise randomly, and variations that are advantageous within an individual’s environment are more likely to be passed down to their offspring. This process is called natural selection. As this process continues from generation to generation, more and more individuals in the population have the advantageous variation of the trait. This can lead to the evolution of new species over time. Although Darwin identified that advantageous and inherited traits lead to evolution, DNA had yet to be discovered, so his theory was incomplete. Neo-Darwinism combines Darwin’s theory of evolution by natural selection with our modern understanding of genes and mutations.

Natural selection is not the only way species evolve. Artificial selection, or selective breeding, is when humans intentionally cultivate desirable traits in a species. Although there have been many recent advancements in biotechnology and gene editing, humans have been manipulating genetics for thousands of years, since the dawn of agriculture. Most of the fruits and vegetables we enjoy today are vastly different from their wild counterparts, and they are the result of humans selectively breeding for mutations beneficial to humans. Through the process of domestication, humans have made foods more palatable and easier to eat. It has also made many of these plant species, such as wheat, dependent on humans for reproduction.

Broccoli, cabbage, kale, cauliflower, and kohlrabi are all crops that evolved from the same ancestor—a wild mustard plant. Humans found a number of traits within that one plant and selectively bred several varieties that now bear little resemblance to their ancestor. Many of the crops we enjoy today were cultivated by Indigenous peoples farming native species. In the Americas, Indigenous farming practices lead to the creation of cacao, potatoes and corn, among other crops.

Mutations and the Environment

Genes do not act alone. Environmental factors, including diet and exposure to pollutants, can cause genetic mutations.

Ultraviolet (UV) light is an environmental factor that can lead to DNA damage in skin cells. UV light can come from the sun or from artificial sources, such as tanning beds. DNA damage from exposure to UV light can cause mutations in how skin cells multiply, which can result in skin cancer, or melanoma.

There is a connection between nutrition and genetics too. Some genetic mutations impact the ability to process certain foods or nutrients. People with phenylketonuria (PKU) have a genetic mutation that impacts how they break down phenylalanine. Phenylalanine is a protein building block, also called an amino acid, found in some foods. PKU causes phenylalanine to build up in the body, which has serious health problems, including nervous system issues and intellectual disability. To avoid these side effects, people with PKU must limit their intake of foods with phenylalanine or take medication. In some countries, genetic testing for PKU is done at birth.

The study of this connection is part of an emerging scientific field called nutrigenomics. People who study nutrigenomics research how our unique genomes affect how we absorb nutrients and how nutrients can impact gene expression and mutations. Rather than looking at specific mutations, nutrigenomics considers the entire genome. It is also important to note that many other factors can contribute to how genetics and nutrition interact. It is important to consider other environmental factors, such as lifestyle.

Mutations and Medical Advancements

Mutations can be a powerful motivator for scientific advancement, especially in medicine. Many medical advancements have resulted from the desire to detect or correct harmful mutations. Services called genetic testing and genetic counseling can help families detect mutations before birth or even before parents pass them on to their offspring. Gene therapies—including gene editing, which alters specific regions of DNA—have the potential to target a range of genetic disorders. Most of these gene therapies are still being tested and are not widely used.

While these advancements hold promise, researching genetic mutations can also have significant societal and ethical impacts. People with genetic disorders from mutations may face discrimination or stigma related to diagnosis, treatment and support of their condition. For example, those with Down syndrome experience a range of misconceptions about the disorder that ultimately lead to discrimination. This discrimination can result in a lack of access to appropriate health care, educational opportunities, employment and community involvement.

In the case of a woman named Henrietta Lacks, a mutation that made her cells valuable for scientific research became a notable instance of bioethical problems and medical racism.

Lacks developed cervical cancer as a result of human papilloma virus (HPV). When Lacks, a Black woman in the United States, was treated for cervical cancer at Johns Hopkins University in 1951, doctors took her cells without her consent and learned that the virus changed her DNA, causing a mutation that allowed her cells to divide indefinitely. Specifically, the virus impacted genes such as p53, which normally regulate cell death and ensure harmful cellular mutations are kept in check. The immortality of her cells came from the undue activation of an enzyme known as telomerase. This enzyme lengthens telomeres, the protective ends of chromosomes that play a role in aging and death as they shorten over time in normal cells.

Lacks’ cells have ultimately informed over 70,000 studies and will likely continue to inform even more. Her cells became one of the most significant cell lines, called HeLa cells, to medical research. Most cells divide around 50 times before dying, but an immortal cell line means scientists can conduct experiments on identical cells indefinitely.

Although this use of a patient’s cells without their permission was the standard practice at the time, Lacks’ family asserted that companies were unfairly profiting from Lacks’ cells and perpetuating racial inequities in medical research. Despite providing a wealth of knowledge to medicine and biotechnology, Lacks and her family were never compensated. Beginning in 2010, media attention, including the book The Immortal Life of Henrietta Lacks and its subsequent movie, brought widespread awareness to the cell line’s origins. The Lacks family has sued pharmaceutical companies involved, including Thermo Fisher, and was awarded a settlement.