Flash cloning

Flash Cloning is a medical process used by the UNSC whereby human body parts are cloned. This usually involves a sample of a subject's DNA, which is used to grow a clone of an organ or body part, which can then be transplanted into the subject where the DNA came from. This way, organ transplants are faster and easier and the rate of success is far higher. Usually, the organ is programmed to grow at an accelerated rate, then to cease rapid development when transplanted into the subject. Therefore, the organ grows quickly and functions properly and efficiently. Since the organ contains the same subject's DNA, there is no threat of rejection by the body.

Human Cloning
While flash cloning entire humans is possible, it is by no means perfect, and it is illegal for someone who is unauthorized to do so. Doing so would result with severe and harsh punishments for violators, and is comparable to modern day child pornography in terms of severity. An embryo is taken and developed a hundred times faster than it would have naturally, becoming something different than it would have been. Many anomalies appear because flash clones are forced to develop too quickly - they have none of the muscle memory, the natural behavioral training most humans get observing people while growing up, of their hosts. They can be trained with intensive therapy to correct this, but after a month or two, they start to degenerate from metabolic instability in a process called "Metabolic Cascade Failure" until they die from various neurological and physiological diseases.

After the future SPARTAN-IIs were kidnapped from their homes, they were replaced by flash clones, intended to explain the sudden disappearance of the SPARTAN-II candidates. Though the flash clones quickly died, they had succeeded in their purpose to draw attention away from ONI and therefore drawing the attention away from the kidnapping. The subsequent Spartan-III Program, based on orphaned children rather than kidnapped ones, was conceived this way also to avoid a repeated violation of bioethics, which was a minor drawback yet major criticism of the SPARTAN-II Program.

Usage for Creating AIs
As an actual human brain is required for the creation of a Smart AI, since a brain is essentially destroyed during the process of creating the AI, the brain of a deceased person is often used. However, Cortana was modeled after the brain of Dr. Catherine Halsey who was obviously still alive. By flash cloning Dr. Halsey's Brain they were able to provide a brain used for the mapping of the AI's "mind" with no undue effects to the donor.