Biologists have long known about the switches, which are clusters of atoms called methyl groups.

生物学家早已知道这个开关，它是由原子组成的，叫做甲基。

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One adds molecules called methyl groups to the DNA of the gene. This suppresses gene expression.

一种是在基因的DNA上添加甲基，从而阻止了基因表达。

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Epigenomics studies the distribution over the genome’s DNA of control molecules called methyl groups.

表观基因组学研究的是分布在控制分子的基因组DNA (叫作甲基群).

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So, you already have a hint that methyl groups are never in the middle, they always have to be on the outside.

那么，你已经得到了一个提示,那就是甲基永远都不可能在中间，它们总是在外侧。

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In particular, when methyl groups (made up of a carbon atom and three hydrogen atoms) are plastered on to a gene, they can stop that gene from being expressed altogether.

ECONOMIST: Genes are not all there is to heredity