表观遗传学（epigenetics）是指在DNA序列不发生变化时，但基因表达却发生了可遗传的改变。

Epigenetics is the study of stable genetic modification that results in changes in gene expression and function without a corresponding alteration in DNA sequence.

简单来说，epigenetics就是通过各种各样的信号刺激之后，我们身体内的各种基因发生了选择性的表达。虽然这是一门新兴的学科，但是在A-level生物中也是非常重要的一部分。

例如我们熟悉的细胞分化（differentiation），就是通过选择性的switch on/off certain gene. 甚至是对与很多疾病的诊断与治疗中，例如癌症，也可以通过研究各种基因的epigenetics，来去诊断具体的病理，究竟是哪一个不该表达的基因表达了还是那一个该表达的基因没有正确表达出来，这样就可以更加具有针对性去进行治疗，这也是未来精准化医疗personalized medicine的发展基础。

接下来我们就来看一下和epigenetics相关的一些关键词吧！

一、Introns and exons  

关键词：内含子；外显子；蛋白表达

In most genes in humans and other multicellular organisms, the protein-coding sequence is split into segments (exons) that are separated by non-coding sequence (introns). 

二、Splicing 

关键词： 剪切；去除内含子；选择性剪切导致蛋白结构改变

When a gene is transcribed, the RNA polymerase traverses the entire sequence, exons and introns, to make the primary transcript. This is then processed, within the nucleus, by being physically cut at exon-intron boundaries; the exons are spliced together to make the mature mRNA, and the introns are discarded. The machinery that does this, the spliceosome, is exceedingly complicated,Alternative splicing is often tissue-specific, and the different splice isoforms may have clearly different functions. 

三、Promoter

关键词：启动子；允许RNA 聚合酶结合；基因可以表达

In order to transcribe a gene, the RNA polymerase must attach to the DNA just upstream of the transcription start site. This region is called the promoter. Binding is determined by the DNA sequence, but also by sequence-specific binding of a whole set of other proteins that together constitute the transcription initiation complex. 

四、Enhancer

关键词：增强子；加强RNA聚合酶结合；促进基因表达

Enhancers are promoter-like sequences that are located some way away from the gene they regulate. They can be upstream or downstream of the gene, and in some cases up to a million base pairs away. Like promoters, they bind a variety of proteins, many of them tissue-specific, and the DNA loops round to bring them into contact with the promoter

五、Methylation and acetylation

关键词：DNA甲基化；乙酰化

Inactive genes can be wrapped tightly and become inaccessible – ensuring they are not read – (epigenetic silencing)

Active genes are ‘looser’ and are more easily read and transcribed

六、DNA methyltransferases

关键词：DNA甲基化酶; 抑制转录

They add methyl (-CH3) groups to DNA, specifically to the 5-position of cytosines that lie immediately upstream of guanines (so-called CpG dinucleotides, the p representing the phosphate joining adjacent nucleotides). 5-methyl cytosine base-pairs with guanine exactly the same as normal cytosine, but the methyl groups act as a signal to methyl DNA binding proteins, which in turn recruit other regulatory proteins.

七、Histone modification

关键词：组蛋白修饰；甲基化或乙酰化；调节基因表达

An acetyl group (-COCH3) is added to one of the lysines in the histone structure.

Open up the structure and activates the chromatins.

A methyl group (-CH3) is added to a lysine. Depending on the position of lysine

Activation or inactivation

以上就是关于调节基因表达的一些常见方法啦，不要忘记记笔记哦