Which feature distinguishes gene-targeted mutation from pronuclear injection?

• A. It results in random insertion of the transgene
• B. It uses non-homologous end joining to integrate at any site
• C. It inserts the transgene at a defined locus using homologous sequences
• D. It cannot create heritable changes

Answer: (C)

The key idea is how the DNA is inserted. Gene-targeted mutations are designed to modify a gene at a specific location by using DNA sequences that match the regions around the target site. This homology guides the cell’s repair machinery to insert or alter the genome precisely at that defined locus, typically through homologous recombination or homology-directed repair. This precise, locus-specific insertion is what sets gene-targeted mutation apart.

In contrast, pronuclear injection introduces DNA into a zygote without precise guidance, so the DNA often integrates at random sites in the genome, with varying copy numbers and insertion orientations. This lack of control over the insertion location is why random integration is a hallmark of pronuclear injection rather than gene-targeted approaches.

So the distinguishing feature is the defined locus insertion using homologous sequences, which is why the correct statement emphasizes targeted, locus-specific modification.