Fraction of cells affected 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 all the internal organs, skin, bones, blood and connective tissue. There are approximately 220 types of somatic cells in the human body. 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 organisms 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.%DIFDELCMD < %DIFDELCMD < %%% Exceptions to inheritance alt=|Hydra oligactis with two buds. Reproduction by budding is an exception the rule that somatic mutations can not be inherited. The definition of a somatic mutation as any mutation that cannot be passed down to offspring is useful in animals that have a dedicated germline to produce reproductive cells. However, it is of little value in understanding the inheritance of somatic mutation in multicellular organisms that do not designate germ cells in early development. Plants and basal animals such as sponges and corals do not have a germline; instead they generate gametes from pluripotent stem cells in adult somatic tissues. In flowering plants, for example, germ cells can arise from adult somatic cells in the floral meristem. Other animals without a designated germ line include tunicates and flatworms. This distinction is also blurred in organisms that can reproduce asexually, without production of gametes. For instance, animals in the cnidarian genus Hydra can reproduce asexually through the mechanism of budding (they can also reproduce sexually). In hydra, a new bud develops directly from somatic cells of the parent hydra. A mutation present in the tissue that gives rise to the daughter organism would be passed down to that offspring.%DIFDELCMD < %DIFDELCMD < %%% Many plants naturally reproduce through vegetative reproduction - growth of a new plant from a fragment of the parent plant - propagating somatic mutations without the step of seed production. Humans artificially induce vegetative reproduction via grafting and stem cuttings.
 %DIFDELCMD < %DIFDELCMD < %%% %DIFDELCMD < %DIFDELCMD < %%% TITTIES
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Fraction of cells affected 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 all the internal organs, skin, bones, blood and connective tissue. There are approximately 220 types of somatic cells in the human body.
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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 organisms 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.
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Exceptions to inheritance alt=|Hydra oligactis with two buds. Reproduction by budding is an exception the rule that somatic mutations can not be inherited. The definition of a somatic mutation as any mutation that cannot be passed down to offspring is useful in animals that have a dedicated germline to produce reproductive cells. However, it is of little value in understanding the inheritance of somatic mutation in multicellular organisms that do not designate germ cells in early development. Plants and basal animals such as sponges and corals do not have a germline; instead they generate gametes from pluripotent stem cells in adult somatic tissues. In flowering plants, for example, germ cells can arise from adult somatic cells in the floral meristem. Other animals without a designated germ line include tunicates and flatworms.
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This distinction is also blurred in organisms that can reproduce asexually, without production of gametes. For instance, animals in the cnidarian genus Hydra can reproduce asexually through the mechanism of budding (they can also reproduce sexually). In hydra, a new bud develops directly from somatic cells of the parent hydra. A mutation present in the tissue that gives rise to the daughter organism would be passed down to that offspring.
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Many plants naturally reproduce through vegetative reproduction - growth of a new plant from a fragment of the parent plant - propagating somatic mutations without the step of seed production. Humans artificially induce vegetative reproduction via grafting and stem cuttings.
TITTIES