Genome editing medaka (IMAGE) Heidelberg University Caption Following successful genome editing of the oca2 gene, the ratio of originally pigmented to unpigmented cells in the embryonic eye of the Japanese ricefish medaka serves as readout for Cas9 efficiency. This was used to optimise the CRISPR/Cas9 system. Low knock-out efficiency of standard Cas9 enzymes (top) and increased knock-out rate using the improved heiCas9 (bottom). Credit Thomas Thumberger (COS) Usage Restrictions This image may be used only in connection with the contents of this press release, and the source of the image must also be cited. License Original content 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.