@tristargod
BSD was created based on the original AT&T UNIX. However, it soon diverged to become independent. There was even a lawsuit over that. Linux was developed completely separate, with Linux Torvalds wanting to create a Unix like OS, after finding MINIX inadequate.
Then we had SCO Unix/Caldera claiming ownership over Linux based on very tenuous claims. One was through IBM, which created JFS for OS/2 and then ported it to AIX, which was then claimed to be a derivative work of UNIX, even though it was originally developed for OS/2. That's the sort of nonsense SCO/Caldera was using to justify their claims. There's lots more.
BTW, this history was covered extensively on Groklaw.