Chromosomes in Mouse Embryo (IMAGE) Howard Hughes Medical Institute Caption A microscopy image of the complete set of chromosomes in a 2-cell stage mouse embryo reveals chemical tags that ,decorate, DNA-packaging proteins called histones. The tag H3K27me3 (shown in green), can switch gene activity off. The tag H3K4me3 (shown in red) can turn gene activity on. White represents the chromosomes' centromeres, and blue represents DNA. Credit Azusa Inoue and Yi Zhang Usage Restrictions Must use with credit. 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.