Leveragen is a Boston-based biotech startup company providing customized genetic modeling services. Our platform technology is CRISPR-facilitated gene targeting in embryonic stem (ES) cells. The key advantage of our approach over direct CRISPR injection in zygotes is that screening for designed mutations is carried out in ES cells before generating mice. The ES cell-based approach is most suitable for creating large fragment knockins (e.g. reporter/Cre/conditional alleles) and complex modifications (e.g. chromosome engineering/conditional point mutations/genomic humanization), for which direct CRISPR injection is either inefficient or impossible. By overriding the needs to maintain a large colony for mutation screens in mice and avoiding repeated injections due to low mutation rate, our approach leads to significant savings in both cost and time.