Do you have any ideas, or at least educated guesses, about how the troll's were mixed ectobiologically speaking? If that makes sense.

We are never told specifically, however there’s minor proof that points to the possibility of Karkat’s Group (Beta Trolls) being hatched first as the Originals, with Kankri’s Group (Alpha Trolls) being the re-combination.

First of all, in this scene we have the Beta Trolls being made first- Implying that the Alphas were the subsequent re-combination, and as such, their spawn. Furthermore, however, there’s this panel.

http://www.mspaintadventures.com/?s=6&p=005370

You wish you never pushed those buttons and hatched your team out of all this goddamn slime. You are no ectobiologist. If only there was some other title more befitting of the true discipline you practice, and the death sentence given to whatever you do the disservice of creating. You can’t think of one though.

And what about the OTHER twelve wigglers you spawned? Who were they? Probably further proof this was all meaningless and random. Could it be that they were the true heroes meant to be sent back to play this game, while your team was the superfluous crop? Could a mistake have been made during the reckoning?

This seems to further confirm the order was, indeed, first the Betas (As Clones of Themselves), and then the Alphas (As made from a recombination of their genes). Curiously enough, Karkat IS sort of right in this instance- There was something that happened during the Reckoning, and that is that the energies of the Scratch ensured they were the Heroes rather than have the Alphas become Players at all, erasing their Timeline. They’re not the rejects. They’re the hope the Alphas gave everything up for.