Mutation

Mutation is the fifth book in the Remnants series by K.A. Applegate.

Back Cover Summary
There is a computer called Mother that runs the ship keeping the remaining members of the human race alive. And that computer has the ability to create imaginary worlds filled with things that don't– can't –exist. The problem is that this computer has evolved. It experiences emotion. And it is out of control.

Jobs, Mo'Steel, 2Face, Billy, and the other Remnants are struggling to survive within Mother's environments. But they are not all surviving. And they've discovered new Remnants–one of which has undergone a strange mutation. A mutation that has made him into a living, breathing, monster...