Genome editing

Genome editing deliberately changes the DNA sequence at selected sites in a genome. Changes can include a small insertion or deletion, replacement of a sequence, or introduction of a specific base change. This differs from merely measuring gene expression or transiently changing it without altering the underlying DNA.

In a common CRISPR-Cas9 approach, a guide RNA directs a nuclease to a matching DNA region, and cellular DNA repair determines the resulting sequence change. Repair can disrupt a gene or use a supplied template to introduce a designed change. Le Cong and colleagues demonstrated programmable targeting of endogenous mammalian sites and simultaneous editing at several sites in 2013.^[ref]

A targeted cut is therefore an intermediate operation, not proof of the intended edit. DNA sequencing of the resulting alleles distinguishes the planned change from unintended repair products.