With sgRNAs targeting the mu and gamma1 switch regions in the Igh-C immunoglobulin heavy chain constant region, the intervening sequence was deleted in ES cells using CRISPR/Cas9 technology. This engineered recombination (deleting the Ighm, Ighd, and Ighg3 segments) mimics an IgG1 class-switch. (J:252910)