[quote=@Stale Pizza]
<Snipped quote by Little_ninja>

1st Episode of the original Sword Art Online arc. When Kayaba appears, and they get changed back to their normal appearances, Klein guesses that the system knew how they looked like: "Did you remember that when you had to install the game, they told you to 'calibrate' your body by touching it all over?" 

[/quote]

That's got nothing to do with genetic information
Not like it's sampling your genes or anything
That's calibrating.
Another user could use it, but the calibration would be off, and the gameplay would probably be awkward, unless they had almost identical builds