siRNA is produced by cleavage of dsRNA templates by DICER, an RNAse III ribonuclease. The siRNA can be incorporated into an RNA-induced silencing complex (RISC) and unwound into single-stranded siRNA. Next, single-stranded siRNA directs the RISC complex to the target mRNA for disruption, causing RNA interference. Depending on the amount of siRNA expressed and its inhibition efficiency, expression of the target gene can be completely blocked or measurably inhibited. This allows researchers to identify and study the function of genes, especially those that are lethal after complete knockout.