In Stargate, there are a number of people who have the Ancients ATA gene which they inherited from being descended from the Ancients that returned to Earth. But my question is has it ever been mentioned how many Humans have the ATA gene ? e.g. there's 500 million Humans or 3 % of the Earths population have the gene.
It's not specifically stated in the show, other than to say that it's rare.
In the follow-on novel; Stargate Atlantis: Legacy: Homecoming, they go into a bit more detail. Some 4% of the human population have the gene naturally expressed (equivalent to around 280M individuals on Earth).
"Fortunately for us, after the last of the Ancients evacuated to Earth they mixed to a certain extent with the human population there. Roughly 4 per cent of humans from Earth have the ATA gene naturally expressed. It’s recessive, and therefore rare"
On top of that, we learn that ATA gene therapy treatment only works on people who have a dormant version of the gene (47% of the population) which means that the total number of people who carry some ancient genes is over 3 billion.
There are more who have successfully used Dr. Beckett’s gene therapy to activate an ATA recessive that they’re carrying, and can utilize Ancient technology to a limited degree, but the naturally expressed ATA gene tends to be stronger and easier for people to learn to use. If you have it, consider yourself very lucky.” Keller picked up her orange juice. “At least until people want you to come turn things on all day. Carson complains all the time that he’s the human light switch.”
Eva searched for words. “Do you have this…gene?”
“No.” Keller’s mouth pinched. “And apparently I don’t carry it as a recessive either, since the gene therapy didn’t work on me. It can’t activate what you don’t have.”