<P> A simple version of the CRISPR / Cas system, CRISPR / Cas9, has been modified to edit genomes . By delivering the Cas9 nuclease complexed with a synthetic guide RNA (gRNA) into a cell, the cell's genome can be cut at a desired location, allowing existing genes to be removed and / or new ones added . The Cas9 - gRNA complex corresponds with the CAS III crRNA complex in the above diagram . </P> <P> CRISPR / Cas genome editing techniques have many potential applications, including medicine and crop seed enhancement . The use of CRISPR / Cas9 - gRNA complex for genome editing was the AAAS's choice for breakthrough of the year in 2015 . Bioethical concerns have been raised about the prospect of using CRISPR for germline editing . </P> <Table> <Tr> <Th_colspan="2"> Cascade (CRISPR - associated complex for antiviral defense) </Th> </Tr> <Tr> <Td_colspan="2"> Structure of crRNA - guided E. coli Cascade complex (Cas, blue) bound to single - stranded DNA (orange). </Td> </Tr> <Tr> <Th_colspan="2"> Identifiers </Th> </Tr> <Tr> <Th> Organism </Th> <Td> Escherichia coli </Td> </Tr> <Tr> <Th> Symbol </Th> <Td>? </Td> </Tr> <Tr> <Th> PDB </Th> <Td> 4QYZ </Td> </Tr> </Table> <Tr> <Th_colspan="2"> Cascade (CRISPR - associated complex for antiviral defense) </Th> </Tr>

Crispr uses pieces of phage dna incorporated into the genome