Ancient Technology Activation gene

The Ancient Technology Activation (ATA) Gene, is a specific gene expression present within the DNA of the Ancients that was used as a sort of "genetic key", so only their kind can operate their technology.

Overview
According to Dr. Beckett, who discovered its existence, the ATA gene is always on, instructing various cells in the body to produce a series of proteins and enzymes that interact with the skin, the nervous system and the brain, allowing gene carriers to operate Ancient technology. Since a small percentage of humans from Earth are descendants of the Ancients, some of them already have this gene.

Some Ancient technology only needs to be "activated" by someone possessing this gene and it remains usable by those without the gene afterward. Some other technology, however, cannot be used by someone without the gene (for example, only those with the ATA gene can interact with the neural interface of a control chair, pilot a Puddle jumper, and use the life signs detector). The ancient technology that requires the gene is amazingly well-protected by it. The Asgard group that attempted to activate the Attero device, the Lost Tribe, had spent hundreds, maybe even thousands of years trying to activate it without the gene with no success.

Not all gene carriers, however, can use the gene in the same way. For most of them, it requires training and practice, but a few can do it easily and intuitively. Lt. Col. John Sheppard and Jack O'Neill are extremly intuitive in fact (Although Jack had access to a Repository of knowledge,) this is why Dr. Weir insisted that Sheppard be part of the Atlantis Expedition.

Starting in 2004, the Atlantis Expedition team began to employ the in vivo retroviral gene therapy (using a deactivated mouse retrovirus) to transfer the Ancient gene expression to humans; however, only about a 47-48% of those who undergo the procedure are rewarded with the ATA gene, and even then it is not always permanent.

Naturally

 * General Jack O'Neill
 * Major/Lt. Colonel John Sheppard
 * Dr. Carson Beckett
 * Sgt. Markham
 * Dr. Kusanagi (mentioned but never seen)
 * Joe Spencer
 * Major Evan Lorne
 * Harmony

By Gene Therapy

 * Dr. Rodney McKay
 * Col. Dillon Everett
 * Some of Col. Everett's troops
 * Lt. Morrison

Unknown Source

 * Lt. Miller
 * Dr. Abrams

Unsuccessful Gene Therapy

 * Dr. Radek Zelenka

Possible Gene
Michael's Hybrids possibly possess the gene, because they were able to move a jumper and use it to infiltrate Atlantis's control room. This is possibly done by the gene therapy. Michael held Carson Beckett's clone prisoner for two years and had him work for him. He possessed the knowledge and Ancient gene of the original Beckett.

Trivia

 * O'Neill and Sheppard apparently have a very strong form of the gene, and operate Ancient technology almost instinctively.
 * It is possible the ATA Gene-produced proteins and enzymes cause the synaptic pathways in the nervous system to generate minute electromagnetic fields that signals Ancient technology to work. However, this has yet to be confirmed.
 * In "Hot Zone", Dr. Zelenka said that the gene therapy only works for 48% of recipients. However, later in "Irresistible" Beckett told Lucius Lavin that the success rate is 47%. The change in percentage could simply be due to results from subsequent recipients.
 * The Atlantis Expedition uses a ranking system called "Chair Interface Aptitude" (or CIA) that ranks people with the ATA gene in the order of their ability to use the Ancient Control chair. The highest ranked person in Atlantis is John Sheppard, followed by cloned Dr. Carson Beckett