Double–Y syndrome was a genetic mutation present in some males in the 22nd century. Specifically, it was a deformity of the X/Y chromosome pair, resulting in the YY pattern. This pattern gave the afflicted person a predisposition for antisocial behavior, specifically brutal crimes including rape and serial murder.
Owing to their dangerous nature, double–Y syndrome convicts were typically detained in separate facilities from other convicted criminals. One such double–Y prison facility was the Fiorina 161 Class C Work Correctional Unit on the Outer Veil planetoid Fiorina 161, which originally housed five thousand inmates.