Cas9 can be easily programmed to make DNA double strand breaks (DSBs) in the genome of cells. These breaks are then repaired by the cells’DNA damage repair mechanisms using either the non-homologous end joining (NHEJ) pathway or the homology-directed recombination or repair (HDR) pathway. However, NHEJ-mediated repair of Cas9-generated breaks might generate random/small insertions and deletions at the targeted site during double-stranded break (DSB) repair. While CRISPR-Pro technology offers a solution to the limitations represented by above method. By utilizing Cyagen’s unique fertilized mouse eggs process, repair of DSBs is prone to occur by HDR pathway. The accuracy and efficiency of DSBs repair are greatly improved, which allows for large fragment knockin (up to 15kb) and conditional knockouts.