The present disclosure relates to methods of producing engineered human cells. Methods may comprise providing a composition for inducing a modification of a target endogenous nucleic acid sequence in a nucleus of a human cell, wherein the composition comprises an amount of a Cas9 protein and an amount of a sgRNA in an in vitro environment free of the human cell. In some embodiments, the amount of sgRNA and the amount of Cas9 protein may be present in the composition at a weight ratio of 4:9 to 4:3. A Cas9/sgRNA complex may form in the in vitro environment prior to being introduced into the human cell. Methods may further comprise introducing the Cas9/sgRNA complex into the human cell via electroporation, wherein the Cas9/sgRNA complex induces the modification of the target endogenous nucleic acid sequence in the nucleus of the human cell.