Assigning Gene function experimentally
Gene function can be assugned experimentally by knocking out a gene or knocking down it's expression and investigating the phenotypes that result.
Different methods are used to knock out a gene, including replacing the normal chromosomal copy of the gene with a disrupted copy (used in many organisms) and inactivating the gene by inserting a transposon into it( typically used in bacteria).
The outcome in either case is a gene with no, or markedly reduced, function.
Gene knockouts made in this way are permanet changes in the chromosome.
Alternatively, gene expression can be silenced (KNOCKED DOWN) in many Eukaryotes at the translation level by RNA interference in which specific small regulatory RNA targets a specific mRNA for degradation.
This method DOES NOT cause permanet change, but prevents the translation of the mRNA of a target gene for as long as the small regulatory RNA molecule is present.