A Historical Perspective on Genetics: From the Classical Era to the Golden Age of CRISPR

Gene editing used to be a subject of science fiction, but is now very much a subject in real life. Since the philosophers of the Classical Era documented their theories on heredity the field of genetics has flourished. The study of trait inheritance would be nowhere without the landmark experiments on pea plants (Pisum sativum) performed by Gregor Mendel in the mid 1800s. The re-emergence of his work, along with several pivotal experiments that connected heredity with DNA led to a widely accepted understanding of genetic principles. It was only a matter of time before scientists were able to edit genes. Cre-lox recombination, adapted from bacteriophage systems, allowed for the insertion, deletion, or translocation of genes, but the infidelity of loxP site recognition prevented it from reaching therapeutic potential. The new goal in gene editing became exploiting the endogenous cellular repair mechanisms— this requires a double-stranded break. The challenge commenced of how to induce such a break in a desired genetic locus. This led to chimeric nucleases such zinc finger nucleases and transcription activator-like effector nucleases (TALENs), in which recognition domains lure a nuclease to a specific site in the genome. These are far more robust than Cre-loxP but rely on imprecise protein-DNA interactions for sequence targeting. CRISPR-Cas gene editing set itself apart by exploiting DNA’s inherent complimentary base pairing capabilities to target a nuclease to a sequence of interest. With the least off-targeting of any previous technique, and the potential to engineer higher specificity, CRISPR-Cas technology has inspired so many prospective applications, thus commencing the Golden Age of gene editing