XL-1 Red Competent Cells can be used to introduce random mutations in a cloned gene of interest through a highly efficient, rapid, and reproducible method. The method involves propagating the cloned gene into XL-1 Red Competent Cells, an Escherichia coli strain deficient in three of the primary DNA repair pathways.The mutS, mutD, and mutT mutations were introduced into the XL-1 Red strain using basic bacterial genetics. The random mutation rate in this triple mutant strain was measured to be ~5000-fold higher than that of the wild-type.