Mice carrying mutations in multiple genes are traditionally generated by 
sequential recombination in embryonic stem cells and/or time-consuming 
intercrossing of mice with a single mutation. The CRISPR/Cas system has been 
adapted as an efficient gene-targeting technology with the potential for 
multiplexed genome editing. We demonstrate that CRISPR/Cas-mediated gene editing 
allows the simultaneous disruption of five genes (Tet1, 2, 3, Sry, Uty--8 
alleles) in mouse embryonic stem (ES) cells with high efficiency. Coinjection of 
Cas9 mRNA and single-guide RNAs (sgRNAs) targeting Tet1 and Tet2 into zygotes 
generated mice with biallelic mutations in both genes with an efficiency of 80%. 
Finally, we show that coinjection of Cas9 mRNA/sgRNAs with mutant oligos 
generated precise point mutations simultaneously in two target genes. Thus, the 
CRISPR/Cas system allows the one-step generation of animals carrying mutations 
in multiple genes, an approach that will greatly accelerate the in vivo study of 
functionally redundant genes and of epistatic gene interactions.