The homing pathway of some group I introns. In this pathway, the gene with the intron (X′) and the same gene without the intron (X) are present in the cell, and an intron-encoded endonuclease creates a double-strand break in the uninterrupted gene (X). The break triggers recombinational DSBR similar to that outlined in Figure 13-2, using the intron-containing gene (X′) as a template for repair. When the repair is complete, both genes have a copy of the intron.