Contact: John Ascenzi
Children's Hospital of Philadelphia
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
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