What are typical outcomes of CRISPR editing in a cell?

• A. Indels causing frameshifts or precise edits via donor DNA through homology-directed repair.
• B. Random mutations across the entire genome.
• C. Complete deletion of the target gene always.
• D. Increased plasmid copy number.

Answer: (A)

CRISPR editing typically produces changes by how the cell repairs the break you’ve made. When Cas9 creates a targeted double-strand break, the cell mainly fixes it with non-homologous end joining, which is fast but error-prone and often adds or removes a few bases right at the cut. Those insertions or deletions—indels—usually disrupt the gene’s reading frame, effectively knocking it out or crippling its function.

If you supply a donor DNA template with matching sequences on either side (homology arms), the cell can use homology-directed repair to copy in the exact sequence from the donor. That allows precise edits, such as restoring a mutation, inserting a tag, or making a specific base change. So the typical outcomes you’d expect are indels that disrupt the gene or precise edits introduced via donor DNA through HDR.

Complete deletion of the gene isn’t guaranteed; editing doesn’t automatically remove the entire gene. Random, genome-wide mutations aren’t the intended result of CRISPR targeting, though off-target effects can occur in some cases. Increased plasmid copy number isn’t a direct outcome of the editing process itself.