Biology · Semester A TEKS 7A-8A
Hard
CRISPR-Cas9 gene editing uses a guide RNA to direct the Cas9 enzyme to a specific DNA sequence, where Cas9 creates a double-strand break. The cell's own repair machinery then fixes the break, sometimes introducing changes (like small insertions/deletions) at that site. What determines WHERE in the genome the edit occurs?
AThe guide RNA has no influence on cut location; only the specific cell type determines where Cas9 acts — an assumption that does not hold once the actual details of this scenario are considered
BThe target location is determined solely by which chromosome is physically closest to the cell's nuclear membrane — a common mix-up that mistakes a related but distinct concept for what is actually happening
CThe sequence of the guide RNA, which is designed to be complementary to the specific target DNA sequence, directs Cas9 to cut at that location and nowhere else (barring off-target effects)
DCas9 cuts DNA entirely at random locations throughout the genome regardless of any guide RNA sequence used — a distortion that swaps the actual cause and effect described in this situation
Explanation
The guide RNA's sequence is designed to base-pair with a specific complementary target sequence in the genome; this base-pairing is what directs the Cas9 enzyme to cut at that precise location (with a nearby PAM sequence also required), giving CRISPR-Cas9 its site-specific gene-editing precision, unlike older, less targeted approaches.
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