Abstract
CRISPR/Cas9 technology has revolutionized genome editing in mice, allowing for simple and rapid development of knockouts and knockins. CRISPR relies on small guide RNAs that direct the RNA-guided nuclease Cas9 to a designated genomic site using ∼20 bp of corresponding sequence. Cas9 then creates a double-strand break in the targeted loci that is either patched in an error-prone fashion to produce a frame-shift mutation, a knockout, or is repaired by recombination with donor DNA containing homology arms, a knockin. This protocol covers the techniques needed to rapidly generate knockout and knockin mice with CRISPR via microinjection of Cas9, the guide RNA, and possible donor DNA into the mouse zygote. © 2018 by John Wiley & Sons, Inc.