a process whereby similar DNA sequences are swapped out. In addition to allowing genomes to integrate new genetic information from the outside (through horizontal gene transfer), it also allows cells to repair damaged DNA based on an undamaged copy (this is called homology-directed repair). It also allows for the generation of genetic diversity even in organisms that only naturally carry out vertical gene transfer – a version of it allows pieces of each biological parent’s chromosomes to mix & match during meiosis (a phase of sexual reproduction), so that offspring inherit some of each of their grandparent’s genes.