Bioethics Blogs

The Science Behind Genome Editing: Laying the Foundation for Ethical Analysis


Genome editing, or the ability to manipulate the DNA of an organism, has been facilitated by gene function studies made possible by the progress and affordability of genome sequencing (Gaj T, et al 2013; Ding Y, et al 2016).  To make ethical decisions regarding evaluation and regulation of new genome editing technologies, it is important to gain an understanding of their mechanisms of action and potential applications.

The scientific community has developed several commonly used genome-editing techniques: zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and clustered regularly interspaced short palindromic repeat (CRISPR). ZFNs, TALENs, and CRISPR all use nucleases (proteins or enzymes that can cleave DNA), which can be customized to recognize a particular sequence of base pairs in DNA. More recently, Gao et al (2016) demonstrated the utility of yet another nuclease, Argonaute, for genome editing. In general, once recognition of the target DNA sequence occurs, the system’s nuclease binds to the DNA and creates breaks in both strands of the DNA, also known as a double-strand break (DSB).

The DSB can then be repaired within the cell through either of two DNA repair mechanisms: error-prone nonhomologous end joining (NHEJ) or homology-directed repair (HDR) (Wyman and Kanaar 2006). NHEJ is usually the default repair mechanism for DSBs in cells and is useful in research, but is prone to producing errors in the repaired DNA. When DSBs need to be repaired with greater precision (e.g. for therapeutic purposes), use of the more accurate repair mechanism, HDR, is recommended (Ding Y, et al 2016; Cortez 2015).

The views, opinions and positions expressed by these authors and blogs are theirs and do not necessarily represent that of the Bioethics Research Library and Kennedy Institute of Ethics or Georgetown University.