19.1.7—Gene editing by insertion, deletion or replacement

Gene editing changes DNA at a chosen site in the genome by inserting, deleting or replacing a sequence. It is a form of genetic engineering, but the aim is a targeted change to the existing genome rather than random insertion of foreign DNA.

1. Identify the target sequence and the faulty DNA change that must be corrected.
2. Direct a nuclease to the target: in the SME-supported CRISPR example, guide RNA determines the specific point and is attached to the Cas9 cutting enzyme.
3. Cut the DNA strands at that selected site.
4. Use the resulting DNA break to insert, delete or replace the faulty sequence with the intended DNA; the exact repair detail is not expanded beyond this course boundary.
5. Check the edited sequence and then ask whether the relevant gene is expressed and produces the intended function.

Targeted gene editing — guide-directed cutting at a selected genome site, followed by insertion, deletion or replacement.
Earlier vector insertion — DNA delivery could insert into other genes, so the location and consequences were less predictable.
Shared boundary — greater targeting improves the location of the intended change, but it does not automatically prove that every cell was edited, that expression is correct, or that the resulting function is safe.

Target recognition → site-specific cut → sequence change → sequence and expression/function checks. The target sequence defines where the edit is made; the edit type determines whether DNA is inserted, deleted or replaced. No foreign DNA is required to remain in the edited genome.

“Targeted” does not mean automatically perfect or automatically functional. This card stays at the SME-supported guide RNA/nuclease and insertion–deletion–replacement level: it does not add other CRISPR proteins, clinical examples, ethical claims, PCR, gel electrophoresis, microarrays or bioinformatics.