Describe how CRISPR-Cas9 works, including the role of PAM and guide RNA, and how off-target effects are addressed.

• A. Cas9 binds RNA and copies it into DNA.
• B. PAM is a protein that recruits Cas9.
• C. Cas9 creates a double-strand break at a target sequence adjacent to a PAM, guided by gRNA; off-targets can occur and are reduced by high-fidelity Cas9 variants.
• D. Cas9 breaks DNA without guidance from gRNA.

Answer: (C)