 In the summer of 1944 at Cold Spring Harbor Laboratory , McClintock began systematic studies on the mechanisms of the mosaic color patterns of maize seed and the unstable inheritance of this <unk> . She identified two new dominant and interacting genetic loci that she named Dissociator ( Ds ) and Activator ( Ac ) . She found that the Dissociator did not just dissociate or cause the chromosome to break , it also had a variety of effects on neighboring genes when the Activator was also present , which included making certain stable mutations unstable . In early 1948 , she made the surprising discovery that both Dissociator and Activator could transpose , or change position , on the chromosome . 
