The Breeding Pens were a bone thrown to Sinister by the high lord Apocalypse in return for meritorious services. Sinsiter was entrusted with the creation of the next generation of homo superior. A generation to be born not by accident, but by design. With the Pens, he was finally able to have a genetic stockpile of both human and mutant alike from which he could spin genetic straw into gold. Sinsiter's own surrogate children of the Elite Mutant Force patrolled and protected the Pens.