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Somatic cell
A somatic (Greek: σὠμα/soma = body) or vegetal cell is any biological cell forming the body of an organism; that is, in a multicellular organism, any cell other than a gamete, germ cell, gametocyte or undifferentiated stem cell.
In contrast, gametes are cells that fuse during sexual reproduction, germ cells are cells that give rise to gametes, and stem cells are cells that can divide through mitosis and differentiate into diverse specialized cell types. For example, in mammals, somatic cells make up all the internal organs, skin, bones, blood and connective tissue, while mammalian germ cells give rise to spermatozoa and ova which fuse during fertilization to produce a cell called a zygote, which divides and differentiates into the cells of an embryo. There are approximately 220 types of somatic cells in the human body.〔
The word "somatic" is derived from the Greek word ''sōma'', meaning "body".
==Evolution==
As multicellularity evolved many times, sterile somatic cells did too. The evolution of an immortal germline producing specialized somatic cells involved the emergence of mortality, and can be viewed in its simplest version in volvocine algae.〔http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3098969/〕 Those species with a separation between sterile somatic cells and a germ line are called Weismannists. However, Weismannist development is relatively rare (e.g., vertebrates, arthropods, ''Volvox''), as great part of species have the capacity for somatic embryogenesis (e.g., land plants, most algae, many invertebrates).〔Ridley M (2004) Evolution, 3rd edition. Blackwell Publishing, p. 29-297.〕〔Niklas, K. J. (2014) (The evolutionary-developmental origins of multicellularity ).〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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