Flash cloning is a medical process performed in human medicine in the 26th century. It is a more advantageous form of cloning where organs or other body parts go through accelerated ageing to match the age of the donor. The process is restricted by the Unified Earth Government and its colonies, however.
Individual organ cloning
The process uses a sample of a human's DNA to grow a cloned organ, which can then be transplanted into the subject that contributed the DNA sample. Usually, the organ is programmed to grow at an accelerated rate and cease rapid development when transplanted into the subject. This makes the method viable in urgent situations, where patients can't afford to spend years waiting for a normal organ to develop. Since the transplanted organ's DNA matches that of the recipient, the risk of transplant rejection is almost completely eliminated.
As with cloned organs, it is possible to flash clone an entire human being. However, the process is imperfect and, likely due to this, their cloning is highly illegal and is compared with possession of child pornography. Flash-cloned humans are, as with organs, age-accelerated to resemble the DNA donor. Though flash clones have been known to possess memories and personality traits of their donors, they may not necessarily be born with motor-skills and thus have walking and speech difficulties. If a clone was created for the purpose of impersonating their donor, this demonstrates a clear flaw.
The biggest fault by far in flash-cloning of humans is metabolic cascade failure, a syndrome characterised by degeneration of the body. Due to the sheer complexity of cloning an entire human, a series of defects show themselves within months. As they accumulate, the clone inevitably dies from degenerative disorders potentially in every organ as the body essentially collapses. Their deaths from this syndrome are inevitable, and many die within a year. Life can be extended further, it should be noted, with Daisy-023's clone surviving in an assisted state for eight years before dying.
Flash cloning was used by the Office of Naval Intelligence as part of the SPARTAN-II Program. To cover-up the abduction of seventy-five children, it was agreed to create flash clones to prevent searches. The families cared for the children until their inevitable deaths with no knowledge of the switch. Due to office politics, this was abandoned in the subsequent SPARTAN-III Program and recruitment of orphans took place instead.
Usage for creating A.I
Because humanity is a Tier 3 civilization and the creation of a "smart" A.I requires the destruction of a human brain, the brain of a deceased person is often used. There is one known exception in the Halo Universe however: Cortana was modeled after an unauthorized flash clone of Dr. Catherine Halsey's brain, thus illegal in the UNSC. The use of a clone allowed the UNSC to provide a brain used for the mapping of the AI's "mind" with no undue effects on the donor.