Genetic engineering is a process in which the DNA of an organism is selectively altered through artificial means. Genetic engineering is 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 is corrective DNA resequencing for genetic disorders. A far more dubious application of genetic engineering is the genetic "enhancement" of individuals to produce improved senses, strength, intelligence, etc.
Human
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 22nd century, even research which could be used to cure critical illnesses. This ban was implimented 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 are allowed to compete in normal society.
Some, including geneticist Arik Soong, argued that it was convenient for humanity to denounce the attempts at genetic "improvement" of humanity and 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 embryoes of a number of Augment children, Soong wrote long treatistes on the subject of genetic augmenations and improvements. His works were routinely taken and destroyed by his jailors, until the intervention of Jonathan Archer, after which they were taken and stored.
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. (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 attempt to secretly have their children genetically modified. (DS9: "Doctor Bashir, I Presume") Unfortunately, most of these operations are performed by unqualified physicians, resulting in severe psychological problems in the children. (DS9: "Statistical Probabilities")
- The Federation seems to apply the ban loosely in the area of officially-sanctioned scientific research. In 2365, the Federation permitted limited genetic research on humans at the Darwin Genetic Research Station. However, the results of these disasterous experiments, which ended up killing the crew of the USS Lantree, may have convinced the Federation to reimpose stricter prohibitions by the 2370s. (TNG: "Unnatural Selection")
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. (VOY: "Lineage")
Dominion
The Founders of the Dominion have performed extensive genetic modifications on their two servant races, the Jem'Hadar and the Vorta, in order for them to better serve their roles and to ingrain a fanatical devotion to the Founders. (DS9: "The Abandoned", "Ties of Blood and Water") Neither species now reproduce in the traditional biological sense. (DS9: "To the Death")
- According to Vorta legend, they were originally ape-like creatures who were gifted sentience by the Founders. (DS9: "Treachery, Faith and the Great River") It is unknown whether the Jem'Hadar have any such ancestral species.
The Dominion also genetically engineer biological weapons, such as the blight they unleashed against the people of the Teplan system. (DS9: "The Quickening")
Suliban
During the 21st century, the Suliban were no more evolved than humans. However, a number of Suliban, from a faction known as the Suliban Cabal, became recipients of some very sophisticated genetic engineering thanks to a mysterious humanoid from the 29th century. These "enhancements" included subcutaneous pigment sacs, a bio-mimetic garment and eyes with compound retinas – which allowed them to see things starship sensors likely could not detect. The Suliban considered these "enhancements" as "progress". (ENT: "Broken Bow")
Klingons
Others
When they were captured by a pre-warp civilization in 2152, Jonathan Archer and Malcolm Reed claimed to be prototypes of a new breed of supersoldiers. (ENT: "The Communicator")
Genetic engineering had been employed on Denobula since the twentieth century, to generally positive effect. (ENT: "Borderland")
The Tosk were engineered by the Hunters to be prey for their traditional hunts. (DS9: "Captive Pursuit")
The Brunali are proficient at genetic engineering, which they use to create modified crops capable of surviving on their Borg-devastated homeworld. However, they also genetically engineer some of their children to produce a pathogen deadly to Borg. These children are then allowed to be assimilated, so that they can spread the infection to their Borg vessels. Icheb was one such child. (VOY: "Child's Play")