Image: Science VU / Visuals Unlimited, Inc. Fruit fly (Drosophila) with legs instead of antennae.

Mutations are usually due to mistakes that are made when cells copy their DNA before dividing and that are not detected by the cell’s repair mechanisms. Other mutations may be caused by outside mutagenic agents such as ultraviolet rays.

Mutations that happen in body cells may cause an illness like cancer. For example, ultraviolet rays from the sun can cause mistakes when your skin cells replicate. If the cell's natural repair mechanisms do not catch all the errors, some of these errors could lead to skin cancer.

Only mutations that happen in germ cells (egg or sperm cells) are passed from parent to offspring. In this case, the mutation will be in every cell of the offspring.

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Types of mutations

Cancers, genes and mutations

Cancer is a disease where cells grow out of control and invade and damage normal tissue. Cancer can begin as a spontaneous genetic change (or mutation) in a single cell. The occurrence of these mutations can be increased by exposure to radiation, to certain kinds of chemicals (called carcinogens), and to certain kinds of viruses (called oncogenic viruses).

Some people are at a higher risk for certain cancers because they have inherited a genetic mutation. For example, BRCA1 and BRCA2 gene mutations are related to an inherited risk of breast cancer and ovarian cancer. Every cancer has its own specific set of mutations that make it unique.

Protein specified by BRCA1 gene.

Breast cancer cell.

For more information, see genetic testing.