The CASPR/Cas9 system is a new, very powerful technique that can knockout genes in mice, flies, and animals that are not accessible to genetic manipulation. If you are trying to remove expression of a presynaptic protein you need to add a guide RNA and Cas9. What does the Cas9 do?

A) Cas9 targets and removes the gene of interest by annealing the flanking regions.
B) Cas9 binds to the gene of interest so that it is targeted for degradation by CASPR.
C) Cas9 creates a double-stranded break in the DNA.
D) Cas9 causes homologous recombination of sites around the targeted gene.