Somatic mutation

A somatic mutation is a change in the DNA sequence of a somatic cell of a multicellular organism with dedicated reproductive cells; that is, any mutation that occurs in a cell other than a gamete, germ cell, or gametocyte. Unlike germline mutations, which can be passed on to the descendants of an organism, somatic mutations are not usually transmitted to descendants. This distinction is blurred in plants, which lack a dedicated germline, and in those animals that can reproduce asexually through mechanisms such as budding, as in members of the cnidarian genus Hydra. While somatic mutations are not passed down to an organism's offspring, somatic mutations will be present in all descendants of a cell within the same organism. Many cancers are the result of accumulated somatic mutations. The term somatic generally refers to the cells of the body, in contrast to the reproductive (germline) cells, which give rise to the egg or sperm. For example, in mammals, somatic cells make up the internal organs, skin, bones, blood, and connective tissue. In most animals, separation of germ cells from somatic cells (germline development) occurs during early stages of development. Once this segregation has occurred in the embryo, any mutation outside of the germline cells can not be passed down to an organism's offspring. However, somatic mutations are passed down to all the progeny of a mutated cell within the same organism. A major section of an organism therefore might carry the same mutation, especially if that mutation occurs at earlier stages of development. Somatic mutations that occur later in an organism's life can be hard to detect, as they may affect only a single cell - for instance, a post-mitotic neuron; improvements in single cell sequencing are therefore an important tool for the study of somatic mutation. Both the nuclear DNA and mitochondrial DNA of a cell can accumulate mutations; somatic mitochondrial mutations have been implicated in development of some neurodegenerative diseases.