Mark Walker, Johns Hopkins University (IMAGE) Johns Hopkins University Caption Lead author Mark Walker, a former graduate student at Johns Hopkins and now a computational biologist at the Broad Institute. Credit Maria Nemchuk/Broad Institute 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.