Genome Editing Using Zinc Finger Nucleases (ZFNs) (image) Children's Hospital of Philadelphia Share Print E-Mail Caption From top, ZFNs on both sides of the DNA strand target a site upstream of the gene where most hemophilia-causing mutations reside. The ZFNs then cut both strands of the DNA double helix. As homologous recombination repairs the break in the strands, a normal copy of the clotting-factor gene (made from the donor template) is inserted into the DNA sequence, resulting in a corrected gene capable of expressing clotting factor. The mutated, nonfunctional gene remains in the DNA but is now harmless. Credit The Children's Hospital of Philadelphia Usage Restrictions None Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.