text: Artificial introduction of long dsRNAs or siRNAs has been adopted as a tool to inactivate gene expression, both in cultured cells and in living organisms. Structural and functional resolution of small RNAs as the effectors of RNA silencing has had a direct impact on experimental biology. For example, dsRNA may be synthesized to have a specific sequence complementary to a gene of interest. Once introduced into a cell or biological system, it is recognized as exogenous genetic material and activates the corresponding RNA silencing pathway. This mechanism can be used to effect decreases in gene expression with respect to the target, useful for investigating loss of function for genes relative to a phenotype. That is, studying the phenotypic and/or physiologic effects of expression decreases can reveal the role of a gene product. The observable effects can be nuanced, such that some methods can distinguish between “knockdown” (decrease expression) and “knockout” (eliminate expression) of a gene. RNA interference technologies have been noted recently as one of the most widely utilized techniques in functional genomics. Screens developed using small RNAs have been used to identify genes involved in fundamental processes such as cell division, apoptosis and fat regulation.