In Chapter 12, the techniques used for editing genomes are discussed, from early gene targeting approaches to highly specific CRISPR and prime editing techniques using engineered nucleases. The development of techniques through zinc-finger nucleases and TALENs is used to set the context for the CRISPR and prime editing methods that have become widely accessible and are used extensively to make changes to genomes. As an alternative to editing the genome, RNA editing offers a different approach that enables modulation of gene expression without complete inactivation or alteration of genes and may be more appropriate in some therapeutic situations. The potential for genome and RNA editing is outlined, and the ethical aspects noted.

CRISPR systems are democratizing scientists’ access to new tools required for uncovering future significant scientific, medical, and technological advances. CRISPR–Cas9, however, is not the only tool being used to edit DNA sequences. Much like the use of different types of airplanes and vehicles for human transportation, so too can different tools be used for gene editing. This chapter examines the evolution and development of the different types of modern genome-editing tools that have enabled the targeted manipulation of genetic sequences. In so doing, it elucidates how genome editing is a logical extension of the genetic manipulation enabled by pioneer recombinant-DNA techniques. The chapter argues that genome editing exists today because recombinant-DNA technology and molecular cloning were developed, promoted, and refined to give rise to avant-garde molecular tools. As it progresses, the chapter allows the reader to rummage through the genome-editing toolbox and focuses on examining the advantages and disadvantages of four distinct categories of genome editing: (1) chemistry-based systems; (2) viral-based editing; (3) nucleases that rely on protein-DNA interactions for DNA targeting—such as meganucleases, zinc-finger nucleases, and TALE nucleases; and (4) RNA-guided, DNA-nuclease systems, which comprise CRISPR–Cas systems.