This can be completed in casual or classic mode and just requires one play and completion of each of the available levels, no medals need to be earned and overall rank doesn't matter either.
* is a semi-boss level that requires 3 DNA antibodys, if the Antibody is grey you'll need to play a level with that enemy type in to earn one.
** is just a boss fight, costing 1-3000 credits depending on the stage and 3 DNA antibodys.
Strength in numbers
Viral Vectors *
The Shadow over Amara **
Lost Colony: 3 (not sure why game and achievement refer to them differently)
The Truth Will Out
The Odd Job
Lava Lake: 3
Thinning the Herd
The Lichfield **
One thing to note is there is no tracking bar for completed missions for this achievement and it can glitch and not pop, I had this problem with Act of Honor . If it doesn't pop when you finish the final mission of the group, reboot the XOne and that should clear it. If not and it doesn't sort itself out then the only way I've seen is to delete the save and redo the missions, this has fixed it everytime but I would recommend leaving it until everything else is completed.