The first is that the aliens left a failsafe system in their DNA in case of uprising/other emergency - when exposed to a certain substance, the triggers in the genes start destroying their bodies. So far, it seems a realistic method might be cancer, but that would probably take too long. I don't want some instant-death code in their DNA, because it seems a little too much. I don't want it to be a virus, because that would probably affect non-rebelling members, and the aliens would've considered that wasteful.
Does anyone have a suggestion for an effective, quick method of killing a person via problems in the DNA, that ideally wouldn't have many telltales? Maybe cancer given a boost somehow? If it helps, it's a problem now not because they've been exposed to the substance but because a mutation has been activating the failsafe randomly. It should also be something that can be "edited out" of the DNA, at least by the aliens, as it wasn't intended to be a permanant feature.
For this, I've been googling things like "dna", "genetics," "interbreeding," "disease," and "mutation" in various combinations, along with a couple (so far) specific diseases, so I could use help on the search terms, too.
The second is that this race has been interbreeding with normal humans, and I've just started wondering if this means that the offspring should have a heightened chance of expressing conditions carried in DNA of the normal parent that the aliens might've removed altogther, or whatever else might arise from having "cleaned" and altered DNA mixed back in with its source. For that one, I'm not even sure of what search terms to use, so any help there is much appreciated!
Thanks for reading.