Editing Functional genomics (section)

====Knock-outs (gene deletions)====
Gene function can be investigated by systematically "knocking out" genes one by one. This is done by either [[gene knockout|deletion]] or disruption of function (such as by [[insertional mutagenesis]]) and the resulting organisms are screened for phenotypes that provide clues to the function of the disrupted gene. Knock-outs have been produced for whole genomes, i.e. by deleting all genes in a genome. For [[essential gene]]s, this is not possible, so other techniques are used, e.g. deleting a gene while expressing the gene from a [[plasmid]], using an inducible promoter, so that the level of gene product can be changed at will (and thus a "functional" deletion achieved).