Genome Editing with CRISPR and Related Systems
Targeted Genome Editing
How CRISPR works
CRISPR-based systems use a guide RNA to bring a nuclease or editor to a specific DNA sequence. The system creates a targeted change by cutting DNA, blocking transcription, or chemically altering bases depending on the platform.
Editing terms
What role does the guide RNA play in CRISPR editing?
The guide RNA base-pairs with the target and brings the editing machinery there.
Correct answer: It directs the nuclease to the target sequence
Which repair pathway is often exploited to create small insertions or deletions after a cut?
NHEJ is error-prone and can introduce indels that disrupt a gene.
Correct answer: NHEJ
Why is HDR generally harder to use than NHEJ?
Cells often favor NHEJ, and precise template-driven repair is less efficient.
Correct answer: HDR is less active in many cells and requires a repair template
Editing strategies
Knockout via NHEJ
- Fast and efficient
- Often creates loss-of-function mutations
Precise edit via HDR
- Can insert or correct a defined sequence
- Usually lower efficiency
Design caution
Off-target activity, mosaicism, and unintended repair outcomes are major concerns when designing genome edits.
What does PAM mean?
A PAM is a short sequence requirement near many CRISPR target sites.
Correct answer: Protospacer adjacent motif