![](/portals/4/Figures_FIG/04-Genetics_FIG/Fig_crispr_genetics_understanding-stemcells.jpg)
Figure: Functionality of the CRISPR / Cas9 system for changing DNA in the nucleus. A RNA (guide RNA) molecule guides the nuclease Cas9 to a specific site in the genome, where Cas9 cuts both DNA strands (double-strand breaks). The repair mechanism of the cell repairs the DNA using a targeted mutation. The addition of a DNA strand can also be used to modify and repair genes.