CRISPR-Cas Systems for Genome Editing: Evolution, Classification, and Applications

The CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) system with its associated proteins has been introduced as an efficient, precise, and multi-purpose tool for genetic manipulation. Originally, it was identified as the adaptive immune system of prokaryotes against phages, relying on the adaptation, expression and processing, and interference for targeted degradation of invasive elements. It has undergone significant evolution in its natural role and when adapted for scientific applications. Different classes and types of CRISPR-Cas systems, based on their structural and functional differences, have been identified so far. Class I CRISPR-Cas systems consist of multi-subunit complexes however, class II systems contain single-effector proteins such as Cas9 and Cas12. The improvements in understanding of their molecular mechanisms have allowed adapting CRISPR/Cas systems into programmable genome-editing tools, turning them into the cornerstone of modern genetic engineering. Applications of CRISPR/Cas span from basic research in various disciplines to applied medical, agriculture, synthetic biology, and biotechnological disciplines. This chapter describes in detail the origin, classification, and applications of this continuously evolving technology, which holds promise for redefining the boundaries of genome science, opening up new avenues of innovation to some of the most tenacious health, agricultural, and environmental problems in the world.