**Introductory Chapter: Modulating Gene Expression - Abridging the RNAi and CRISPR-Cas9 Technologies**

Aditi Singh

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.84229

**1. Gene-silencing technologies over the years**

Silencing a gene by deleting it, knocking it down, or simply disabling its function has proven to be a promising tool for understanding the function of the gene and to enable lead optimization during drug development process. In recent times, the two commonly used gene modification methods that have been heavily explored are RNA interference (RNAi) and the revolutionary CRISPR/Cas9 system.-

RNA interference (RNAi) is a widely used technology for gene-silencing and has become a critical tool for repression of gene expression which is effectively utilized in various researches. Of late, the mechanism of RNA interference has been well investigated, and undergone various levels of optimization for improving its effectiveness and efficiency.-

The clustered regularly interspaced short palindromic repeats (CRISPR)-associated Cas9/- gRNA system on the other hand, is a unique, targeted genome-modification technique derived from prokaryotic immune system. The cutting edge research and technology advancements in recent years have enabled the CRISPR-Cas9 system to become a popular tool for introducing heritable, precised, insertions and deletions in the eukaryotic genome.
