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 could imagine strategies where you have multiple resistance genes on a plasmid, resistance to Ampicillin, to Penicillin, to Erythromycin for example, and you design strategies for separating out which cells are carrying the plasmid that you're interested in.

若质粒上有多种抗性基因,你就有很多筛选方法,例如对氨苄青霉素,青霉素,红霉素的抗性,而且你可以设计方法分离出,含有你感兴趣质粒的细胞

耶鲁公开课 - 生物医学工程探索课程节选