RNA interference (RNAi) is a process in which RNA molecules are used to inhibit gene expression or silence genes. RNAi occurs naturally in plants and animals and has been harnessed as a tool for biotechnology and medicine. RNAi is triggered by the presence of double-stranded RNA (dsRNA). When dsRNA is introduced into a cell, it is processed by an enzyme called Dicer into small interfering RNA (siRNA). SiRNA consists of two strands of RNA that are complementary to each other and bind to each other to form a double-stranded molecule.