The transfer of genetic material ‘sideways’ between organisms of different species or strains, instead of ‘vertically’ from parent to offspring. It is common among bacteria, in which genes can be transferred via plasmids or through transduction by bacteriophages. An important clinical example is the lateral transfer of genes for antibiotic resistance, which can transform the recipient bacterial cell line and make infection harder to treat. To a lesser extent, eukaryotes also acquire new genes from other species; sometimes these confer selective advantage, in other cases they can cause harm. For instance, the ancestral endosymbiotic prokaryotes that became the mitochondria and chloroplasts of eukaryotes gave marked selective advantage to their eukaryote hosts, and their genes have subsequently mostly been transferred to the nuclear genome and become stably inherited. Infecting viruses integrate into their host chromosomes and can introduce foreign DNA from other species. Bacteria can also transform the genome of cells they infect and may lead to disease, as in the case of plant tumours arising from infection with Agrobacterium tumefaciens. Genetic engineering, e.g. using genome editing, is a way of artificially introducing novel genetic material. See also reticulate (sense 2).