DNA And Gene Expression Practice Test

CRISPR-Cas9 edits targeted DNA by using a guide RNA to locate a specific sequence, and Cas9 then makes a clean double-strand break at that site. After the cut, the cell fixes the break mainly through two pathways. Non-homologous end joining quickly rejoin the ends and is error-prone, which often creates small insertions or deletions called indels that can disrupt gene function. If a donor DNA template is provided, the cell can use homology-directed repair to copy the template into the genome, allowing precise changes such as specific base substitutions or insertions. These outcomes reflect how editing works in practice: gene disruption via indels from NHEJ or precise edits via HDR with a template. Other statements miss the mechanism—for example, Cas9 does not randomly integrate plasmids, does not repress transcription merely by binding promoters, and does not replicate the genome.