Gene mutations can be either inherited from a parent or acquired. A hereditary mutation is a mistake that is present in the DNA of virtually all body cells. Hereditary mutations are also called germline mutations because the gene change exists in the reproductive cells (germ cells) and can be passed from generation to generation, from parent to newborn. Moreover, the mutation is copied every time body cells divide.
Acquired mutations, also known as somatic mutations, are changes in DNA that develop throughout a person's life. In contrast to hereditary mutations, somatic mutations arise in the DNA of individual cells; the genetic errors are passed only to direct descendants of those cells. Mutations are often the result of errors that crop up during cell division, when the cell is making a copy of itself and dividing into two. Acquired mutations can also be the byproducts of environmental stresses such as radiation or toxins.
Mutations occur all the time in every cell in the body. Each cell, however, has the remarkable ability to recognize mistakes and fix them before it passes them along to its descendants. But a cell's DNA repair mechanisms can fail, or be overwhelmed, or become less efficient with age. Over time, mistakes can accumulate.