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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Small chemicals called methyl groups bind to the DNA, helping to determine which genes become active.

被叫做甲基群的小东西附着在DNA上，用以帮助决定哪些基因激活。

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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。

youdao

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。

麻省理工公开课 - 化学原理课程节选

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