A DNA resequencer is a device built by the Ancients.
The resequencer is used to alter the DNA and Brain chemistry of the subject, acceletating the subjects evolution. It is a gradual process, where one has to get used to the changes to the body. Nirrti used a resequencer on the subjects of P3X-367 during her experiments to find a hok'taur to serve as a host for her. While her experiments gave the subjects advanced powers, they also resulted in mutating their physical appearances. Anubis used a resequencer on Khalek to evolve him to a point where he would almost ascend. (SG1: "Metamorphosis", "Prototype")