Turtles all the way down.
No, our DNA fits in too well with all other life forms on earth. You can follow our evolution backwards back to unicellar life forms. Perhaps DNA was introduced here from elsewhere (panspermia, directed or otherwise), but that theory doesn't really offer answers to any questions, it just postpones them.
No, we came from right here, as does every known life form on this planet. If we were seeded, then we were all seeded, about 3.5 billion years ago.