CRISPR/Cas9 gene editing
The URL has a longer form explanation with diagrams.
The really short description is as follows:
The CRISPR/Cas9 technique takes advantage of a particular way bacteria chop up foreign DNA. This mechanisms has been adapted to facilitate disruption of targeted sequences in model organisms such as mice and zebrafish.
Let's say one wants to disrupt gene P.
Research findings have identified rules that govern the location of the targeting such that one can design a short sequence of DNA that will bind to a specific target site within gene P. In the design, in addition to the target sequence, a guide sequence that will bind the Cas9 enzyme is included contiguously.
Thus, this sequence (1) binds to the target site on gene P and (2) permits the guide sequence to tether Cas9 to that target and Cas9 cuts the target DNA sequence.
After the sequence is cut, DNA repair enzymes enter the picture to fix the lesion. The repair is not perfect introducing some combination of sequence deletions or insertions. The exact nature of the repair is assessed by DNA sequencing technology to see if the desired mutation has been introduced.
This technology also permits the introduction of desired sequences into the disrupted gene in a modification of this procedure.
One can search the internet for many explanations and diagrams of this method.