Explain how CRISPR works and how it can be used in genome editing.

CRISPR is based on a type of restriction enzyme that is guided to DNA by a piece of RNA. The enzyme cuts the DNA wherever its "guide" RNA hybridizes. Then, a piece of DNA that includes a template sequence is used to repair the break. Here is the important part: The RNA and DNA can be designed to precisely target and change (respectively) essentially any part of a genome in a living cell. Researchers deliver all three molecules into cells; for example, in the form of genes carried by a plasmid expression vector. A cell that expresses the genes will have both of its chromosomes edited, and the change will be passed to all the cell's descendants.