A portrait of Khan Noonien Singh, a man who was a product of genetic engineering

Genetic engineering, or genetic manipulation was a process in which the DNA of an organism was selectively altered through artificial means. Genetic engineering was often used to produce "custom" organisms, such as for agricultural or medical purposes, as well as to produce biogenic weapons. The most common application of genetic engineering on intelligent beings in the Federation was corrective DNA resequencing for genetic disorders. A far more dubious application of genetic engineering was the genetic enhancement of individuals to produce improved senses, strength, intelligence, etc.

During Earth's 20th century, efforts to produce "superhumans" resulted in the Eugenics Wars. Genetically engineered individuals such as Khan Noonien Singh attempted to seize power. (TOS: "Space Seed")

This would lead to the banning of genetic engineering on Earth by the mid-22nd century, even research which could be used to cure critical illnesses. This ban was implemented because of the general fear of creating more tyrants such as Khan. It was also felt that parents would feel compelled to have their children genetically engineered, especially if "enhanced" individuals were allowed to compete in normal society.

Some, including geneticist Arik Soong, argued that it was simply convenient for humanity to denounce the attempts at genetic "improvement" of humanity, that it was inherently evil because of the Eugenics Wars. He argued that the source of the problem, in fact, wasn't the technology, but humanity's own inability to use it wisely. Imprisoned for, among other crimes, stealing the embryos of a number of Augment children, Soong wrote long treatises on the subject of genetic augmentations and improvements. His works were routinely taken and placed into storage (although his jailers often told him that his work was vaporized). Captain Jonathan Archer expressed his hope to Soong that research into genetic engineering that could cure life-threatening diseases would someday be resumed. (ENT: "Borderland", "The Augments")

Others, however, chose to establish isolated colonies, as became the case with the Genome colony on Moab IV, which was established in 2168. It became a notable and successful example of Human genetic engineering in which every individual was genetically tailored from birth to perform a specific role in society. However, after a five-day visit by the USS Enterprise-D when the ship came to the colony in an effort to save it from an approaching neutron star which, eventually, the craft was able to effectively redirect twenty-three colonists left the colony aboard the craft, possibly causing significant damage to the structure of their society. The reason for the societal split was that those who left the colony had realized their organized, pre-planned world had certain limitations, lacking opportunities to grow that were offered by the Enterprise. (TNG: "The Masterpiece Society")

By the 24th century, the United Federation of Planets allowed limited use of genetic engineering to correct existing genetically related medical conditions. Persons known to be genetically enhanced, however, were not allowed to serve in Starfleet, and were especially banned from practicing medicine. (TNG: "Genesis", DS9: "Doctor Bashir, I Presume")

Nevertheless, some parents attempted to secretly have their children genetically modified. (DS9: "Doctor Bashir, I Presume") Unfortunately, most of these operations were performed by unqualified physicians, resulting in severe psychological problems in the children due to their enhancements being only partially successful, such as a patient's senses being enhanced while their ability to process the resulting data remained at a Human norm. (DS9: "Statistical Probabilities")

In some cases, genetic engineering can be permitted to be performed in utero when dealing with a developing fetus to correct any potential genetic defects that could handicap the child as they grew up. Chakotay's family history included a defective gene that made those who possessed it prone to hallucinations, the gene afflicting his grandfather in Chakotay's youth, although the gene was suppressed in Chakotay himself. (VOY: "The Fight") In 2377, The Doctor performed prenatal genetic modification on Miral Paris to correct a spinal deviation, a congenital defect that tends to run in Klingon families; Miral's mother had undergone surgery to correct the defect in herself at a young age. (VOY: "Lineage")

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