Ancient Technology Activation gene

the Ancient Technology Activation gene (usually spoken as the ATA Gene), is a specific gene expression present in Ancients that is used as a sort of "genetic key", so only their kind can operate their technology. According to Dr. Beckett, who discovered the existence of this gene, 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 the 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 pilot the Puddle Jumpers).

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 (like Major Sheppard) can do it easily and intuitively (in fact, this is why Dr. Weir insisted that he be part of the Atlantis expedition).

In the episode "Hide and Seek", 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 48% of those who undergo the procedure are rewarded with the ATA gene.

Naturally

 * General Jack O'Neill ("Lost City (Part 1)")
 * Major/Lt. Colonel John Sheppard ("Rising")
 * Dr. Carson Beckett ("Rising")
 * Sgt. Markham
 * Dr. Kusanagi (mentioned but never seen)
 * Joe Spencer ("Citizen Joe")

By Gene Therapy

 * Dr. Rodney McKay ("Hide and Seek")
 * Col. Dillion Everett ("The Siege (Part 2)")
 * Some of Col. Everett's troops.

Unknown Source

 * Lt. Miller (Miller piloted a Jumper in "The Siege (Part 1)", which means he has the gene, but it's not mentioned how he acquired it).
 * Major Lorne (Lorne piloted a Jumper in "Condemned").

Unsuccessful Gene Therapy

 * Dr. Radek Zelenka ("Hot Zone")