There are multiple mechanisms that a cell can use to decide which genes it is expressing at any one time and which ones are not expressed.

在某一时刻,决定细胞中哪些基因表达,哪些基因不表达的机理十分复杂

耶鲁公开课 - 生物医学工程探索课程节选

You use it all the time, but maybe along one dimension.

你也许在一维空间里一直在用它

耶鲁公开课 - 基础物理课程节选