|
Epigenetics is the study, in the field of genetics, of cellular and physiological phenotypic trait variations that are caused by external or environmental factors that switch genes on and off and affect how cells ''read'' genes instead of being caused by changes in the DNA sequence.〔(【引用サイトリンク】url=https://icahn.mssm.edu/research/institutes/friedman-brain-institute/research/epigenetics )〕 Hence, epigenetic research seeks to describe dynamic alterations in the transcriptional potential of a cell. These alterations may or may not be heritable, although the use of the term "epigenetic" to describe processes that are not heritable is controversial.〔 Unlike genetics based on changes to the DNA sequence (the genotype), the changes in gene expression or cellular phenotype of epigenetics have other causes, thus use of the prefix ''epi-'' (Greek: ''επί''- over, outside of, around).〔Carey N. (2011): Epigenetics revolution: How modern biology is rewriting our understanding of genetics, disease and inheritance. Icon Books, London, ISBN 978-1-84831-315-6; ISBN 978-1-84831-316-3.〕 The term also refers to the changes themselves: functionally relevant changes to the genome that do not involve a change in the nucleotide sequence. Examples of mechanisms that produce such changes are DNA methylation and histone modification, each of which alters how genes are expressed without altering the underlying DNA sequence. Gene expression can be controlled through the action of repressor proteins that attach to silencer regions of the DNA. These epigenetic changes may last through cell divisions for the duration of the cell's life, and may also last for multiple generations even though they do not involve changes in the underlying DNA sequence of the organism; instead, non-genetic factors cause the organism's genes to behave (or "express themselves") differently. One example of an epigenetic change in eukaryotic biology is the process of cellular differentiation. During morphogenesis, totipotent stem cells become the various pluripotent cell lines of the embryo, which in turn become fully differentiated cells. In other words, as a single fertilized egg cell – the zygote – continues to divide, the resulting daughter cells change into all the different cell types in an organism, including neurons, muscle cells, epithelium, endothelium of blood vessels, etc., by activating some genes while inhibiting the expression of others. ==Definitions== The term ''epigenetics'' in its contemporary usage emerged in the 1990s, but for some years has been used in somewhat variable meanings. A consensus definition of the concept of ''epigenetic trait'' as "stably heritable phenotype resulting from changes in a chromosome without alterations in the DNA sequence" was formulated at a Cold Spring Harbor meeting in 2008. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Epigenetics」の詳細全文を読む スポンサード リンク
|