CRISPR-Cas9: Clustered regularly interspaced short palindromic repeats are segments of prokaryotic DNA containing short, repetitive base sequences. These play a key role in a bacterial defence system,and form the basis of a genome editing technology known as CRISPR/Cas9 that allows permanent modification of genes within organisms. The CRISPR/Cas system is a prokaryotic immune system that confers resistance to foreign genetic elements such as those present within plasmids and phages that provides a form of acquired immunity. It is a unique technology that enables geneticists and medical researchers to edit parts of the genome by removing, adding or altering sections of the DNA sequence.