Chromosomes (IMAGE) Johns Hopkins Medicine Caption When mice were given the drug doxycycline (+Dox), their levels of the protein Plk4 increased, causing too many centrioles to form (pink). The extra centrioles made it hard for the cells to divide efficiently and properly separate their chromosomes (blue). Credit Michelle Levine 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.