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 the sgRNA may be present in the composition in at least a two-fold molar excess over the amount of the Cas9 protein. 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.