What Is a Mutation?

Mutations are permanent alterations in the DNA sequence. They result from changes in the structure of an encoded protein—including a decrease or complete loss of its expression—as a DNA sequence is being copied. Mutations can either be inherited from a person's biological parents, or acquired after birth, typically caused by environmental triggers.

How Mutations Happen

In order to understand how mutations work, it's important to take a step back and revisit the basics of deoxyribonucleic acid—better known as DNA. DNA provides instructions for organisms—including humans—on how to develop, survive, and reproduce. In order for this to happen, DNA sequences—known as "genes"—are converted into proteins. Under certain circumstances, the structure of an encoded protein can change when a DNA sequence is being copied, resulting in a mutation. Additionally, exposure to ionizing radiation or chemicals called mutagens, or infection by viruses may also cause mutations.

Mutations range in size, from a single DNA building block, to a large segment of a chromosome that incorporates multiple genes. They can also have different types of impacts, with some being harmful, while others are beneficial, or have no effect.

Types of Mutations

There are two types of mutations: inherited and acquired. Inherited or hereditary mutations—also known as "germline mutations"—occur in eggs and sperm, and are passed down to offspring. Acquired or "somatic" mutations happen at some point during a person's life, and frequently are the result of environmental factors. Here is more information on each type.

Inherited Mutations

Inherited or hereditary mutations are exactly what they sound like: mutations passed down from a biological parent. Inherited mutations are with a person for life, and are present in nearly every cell in their body. They are also sometimes referred to as "germline mutations" because they are present in a biological parent's eggs or sperm, which are also known as germ cells. Once an egg is fertilized by sperm, it receives DNA from both parents. If this inherited DNA happens to include a mutation, it will be present in each of the resulting child's cells.

Acquired Mutations

Acquired—or somatic—mutations are the result of something that happens during someone's lifetime. Unlike inherited mutations, acquired mutations are only present in certain cells, as opposed to every cell in a person's body. Acquired mutations are most frequently caused by environmental factors such as ultraviolet radiation from the sun and cigarette smoke, or from exposure to ionizing radiation or chemicals called mutagens. Lastly, a person becoming infected by certain viruses may also cause mutations.

When acquired mutations happen in cells other than egg and sperm cells, they can't be passed down to the next generation. What they can do, though, is stick around for the rest of a person's lifetime. For example, if a person somehow got a mutation in the skin cells on their knee, and then later scraped their knee, the new cells their body would create to replace the old ones would contain the mutation. In these cases, though, the mutation dies with them and isn't passed along to any future offspring.

The Significance of Mutations

Genetic mutations play a major role in humans' health, beginning with their development. For instance, if an embryo contains certain severe mutations, it may not survive an entire pregnancy. Typically, this occurs when the mutations occur in genes that are integral to embryonic development, and often disrupt the process early on during the gestation period.

When a person is born with a genetic mutation, it can have a significant impact on their health. In order to keep a human body functioning properly, each of their cells rely on thousands of proteins performing a specific task at a certain time. But in some cases, mutations can prevent one or more of these proteins from carrying out their tasks correctly, causing them to malfunction, or be missing from the cell entirely. This can result in a genetic disorder.

Conditions Associated With Mutations

There are three types of genetic disorders:

• Single-gene disorders: Where a mutation affects one gene; e.g. sickle cell anemia.
• Chromosomal disorders: Where chromosomes—or parts of chromosomes—are missing or altered; e.g. Down syndrome.
• Complex disorders: Where there are mutations in two or more genes, sometimes resulting from a person's lifestyle and environment, e.g. colon cancer

Previously, it was thought that a maximum of 3% of all human diseases were caused by errors in a single gene. But more recent research indicates that this is an underestimate and that there are genetic links to conditions including Parkinson's disease, Alzheimer's disease, heart disease, diabetes, and several different types of cancer. Some genetic conditions result from a problem with a single gene, including phenylketonuria (PKU), cystic fibrosis, sickle cell disease, Tay-Sachs disease, color blindness and achondroplasia (a type of dwarfism).

A Word From Verywell

Not all mutations have a negative impact on human health. In fact, only a small percentage of mutations cause genetic disorders—most have no major consequences for a person's health or an embryo's development. And in some cases, where mutations could potentially cause a genetic disorder, they are repaired by enzymes before the gene is expressed and an altered protein is produced.

Finally, there are rare circumstances where certain mutations can positively affect a person's health—specifically, when new versions of proteins can help someone better adapt to environmental changes. One example of this is a mutation that results in a protein that has the ability to protect a person from a new strain of bacteria.