Epigenetics 表觀遺傳學
In biology, and specifically genetics, epigenetics is the study of heritable changes in gene activity that are not caused by changes in the DNA sequence; it also can be used to describe the study of stable, long-term alterations in the transcriptional potential of a cell that are not necessarily heritable. Unlike simple genetics based on changes to the DNA sequence（the genotype）, the changes in gene expression or cellular phenotype of epigenetics have other causes.
The name epi-（Greek: επί- over, outside of, around）-genetics.
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.
In 2011, it was demonstrated that the Methylation of mRNA plays a critical role in human energy homeostasis. The Obesity-associated FTO gene is shown to be able to demethylate N6-methyladenosine in RNA. This discovery launched the subfield of RNA epigenetics.
表觀遺傳學（Epigenetics），又稱「擬遺傳學」、「表遺傳學」、「外遺傳學」以及「後遺傳學」（Epigenetics），在生物學和特定的遺傳學領域，其研究的是在不改變DNA序列的前提下，通過某些機制引起可遺傳的基因表達或細胞表現型的變化。
表觀遺傳學是20世紀80年代逐漸興起的一門學科，是在研究與經典的孟德爾遺傳學遺傳法則不相符的許多生命現象過程中逐步發展起來的。
表觀遺傳現象包括DNA甲基化、RNA干擾、組蛋白修飾等。與經典遺傳學以研究基因序列影響生物學功能為核心相比，表觀遺傳學主要研究這些「表觀遺傳現象」建立和維持的機制。其研究內容主要包括兩類，一類為基因選擇性轉錄表達的調控，有DNA甲基化、基因印記、組蛋白共價修飾和染色質重塑；另一類為基因轉錄後的調控，包括基因組中非編碼RNA、微小RNA、反義RNA、內含子及核糖開關等。
表觀遺傳學指基因組相關功能改變而不涉及核苷酸序列變化。例如DNA甲基化和組蛋白修飾，兩者均能在不改變DNA序列的前提下調節基因的表達；阻遏蛋白通過結合沉默基因從而控制基因的表達。這些變化可能可以通過細胞分裂而得以保留，並且可能持續幾代。這些變化都僅是非基因因素導致的生物體基因表現（或「自我表達」）的不同，由於目前尚不清楚組蛋白的化學修飾是否可遺傳，有人對於用此術語描述組蛋白化學修飾提出了異議。
表觀遺傳學在真核生物中主要表現在細胞分化過程。在胚胎形態形成過程中，全能幹細胞將分化成完全不同的細胞，也就是說，一個受精卵細胞分化出各種不同類型的細胞，包括神經細胞、肌肉細胞、上皮細胞、血管內皮細胞等，並通過抑制其他細胞和激活相關基因而進行持續的細胞分裂。
2011年的相關研究已證實，mRNA甲基化對人體內能量平衡發揮著至關重要的作用，對RNA上的N6-甲基腺苷進行脫甲基治療可控制FTO基因相關肥胖症，並因此而開創了RNA表觀遺傳學的相關領域。
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