Chapter 5: Genetic Perturbation Methods, from the ‘Awesome Power’ of Yeast Genetics to the CRISPR Revolution

The clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 system enables precise editing of the human genome at scale; a technical revolution with a profound impact on many aspects of drug discovery. CRISPR-Cas9 dramatically improves our ability to perform forward genetics in mammalian cells in high throughput. High throughput genetic perturbation methods are of fundamental importance to drug discovery, and conceptually the impact of these approaches falls into two areas: (1) screens aimed at identifying new components of biological systems that can be the target of new therapeutic approaches; and (2) screening to identify the efficacy target of bioactive small molecules. The foundational concepts of functional genomics were initially established using yeast genetics, and often novel technologies and approaches were first identified in bacteria or lower eukaryotes before the transfer of the approach to mammalian systems. This chapter presents a historical perspective on important high throughput genetic perturbation methods, including yeast genetics, haploid genetic screens, and siRNA. It then focuses on the rapid progress in the development of CRISPR based editing in high throughput and the tremendous potential CRISPR creates to carry out true loss of function genetic screening in mammalian cells.