Homology-directed repair (HDR)

A way for a cell to repair a break in its DNA by “patching” it with a piece of donor DNA. The donor DNA must contain similar sequences, or homology, to the broken DNA ends for it to be incorporated. HDR is a more precise repair pathway than non-homologous end joining. In genome engineering, a researcher designs and adds in the donor DNA, potentially allowing scientists to replace a disease-causing gene with a healthy copy.