What is the difference between CRISPR and RNAi (RNA interference)?

RNAi is one of the most extensively used reverse genetics approaches to study gene function. Synthetic small RNAs, including short-interfering (siRNA) and short-hairpin (shRNA), are incorporated into a cell’s RNA induced silencing complex (RISC), which targets mRNA degradation and downregulates protein levels.

Compared to CRISPR, the cost of experiments for RNAi can be low when using cells or simple animal models such as C. elegans. The loss of function is reversible and time taken to achieve the desired phenotype can be relatively short. Using RNAi is relatively easy, but disadvantages include high rates of off-target effects and the presence of hypomorphic phenotypes.1 Hypomorphic phenotypes do not necessarily reflect the loss of function seen with genetic mutations which RNAi is trying to recapitulate.

1. M. Boettcher and M.T. McManus, "Choosing the Right Tool for the Job: RNAi, TALEN or CRISPR," Mol Cell 58(4):575-585, 2015.