"As a final safeguard, Guilliman tasked the Adeptus Terra on Earth with setting up and maintaining genetic banks to produce and store tithes of Space Marine gene-seed. These banks were to provide all new gene-seed for subsequentFoundings of Space Marine Chapters. To prevent cross-contamination, the genetic stock of each Legion was isolated whilst that of the Traitor Legions was placed under a time-locked stasis seal, though at the time many believed they had been destroyed. By taking direct control of these genetic tithes, the Adeptus Terra could ultimately control the Space Marines. They alone had the power to destroy or create Space Marine armies at will."
"The genetic banks used to cultivate the organ implants that turn a normal man into a mighty Astartes would be carefully monitored, and cultivated organs would be subject to the most stringent tests of genetic purity. Young Initiates would undergo rigorous trials of physical and psychological suitability before they were accepted, and only those of the highest calibre would be chosen. On Terra, the Adeptus Terra created genetic repositories to produce and store Space Marinegene-seed. These banks were used to provide new gene-seed for the creation of new Space Marines and, to prevent cross-contamination, the genetic material of each of the old Legions was isolated. Henceforth, the new Space Marine Chapters would receive gene-seed only from their own genetic stock. The suspect gene-seed of the Traitor Legions was placed under a time-locked stasis seal, although at the time, many believed these dangerous stocks of tainted genetic material had been destroyed."