RNAi (RNA interference) is a biological process in which a double-stranded RNA molecule silences the expression of a specific gene by triggering the degradation of its messenger RNA (mRNA) product. RNAi is a powerful tool for studying gene function, as well as for developing new treatments for diseases.

The RNAi mechanism involves small RNA molecules, called siRNAs (small interfering RNAs) or miRNAs (microRNAs), which are complementary to specific mRNA sequences. The siRNA/miRNA binds to the mRNA molecule and recruits a protein complex called the RNA-induced silencing complex (RISC). The RISC then cleaves the mRNA molecule, preventing it from being translated into protein.

RNAi has a wide range of applications, including genetic research, drug discovery, and gene therapy. For example, RNAi can be used to screen large numbers of genes to identify those that are involved in a particular disease process. RNAi-based drugs can also be developed to target specific disease-causing genes, and clinical trials have shown promising results for the treatment of diseases such as macular degeneration and hepatitis B.