Choosing the vector(s) you'll use to express the two critical components needed for CRISPR/Cas9 genome editing, the guide RNA and the Cas9 nuclease, is an important step in your experimental design. Many researchers prefer to use an all-in-one vector that will drive expression of gRNA and Cas9 in a 1:1 ratio. All-in-one vectors may also contain selection markers, such as fluorescent proteins or genes conferring antibiotic resistance, which can make it easier to isolate desired genome-edited clones. You may prefer to express the gRNA and Cas9 from separate vectors, for example if you want to vary the gRNA:Cas9 ratio, or if you want to screen a pool of gRNAs or use a larger gRNA library.
