Clock Genes Peak (IMAGE) University of Pennsylvania School of Medicine Caption This graph shows the time of day when clock genes peak by organ. Credit John Hogenesch, PhD, Perelman School of Medicine, University of Pennsylvania; PNAS Usage Restrictions None License Licensed 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.