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As of late I’ve been developing a concept for a species able to transmit traits through genetic information, basically putting that information into a “host” organism to enact some sort of epigenetic change and “teach” the information encoded in the genetic material. The incompatibility of different XNA systems has troubled me a bit there, though, since I’ve wanted this concept to be something that can be used across diverse species boundaries. (Note that, if it makes a difference, this genetic material doesn’t have to be fully integrated into the host’s systems and replicated or spread by their own cells; it just needs to be accessible and readable so the host understands what it’s “telling” them.)

So about some sort of universal genetic material structure—or perhaps like a type of genetic material that basically consists of multiple pieces/segments equivalent to other types’ coding—which could include code for certain information in multiple “languages” of different biochemistries (for example, one section or piece coding for a trait in our earthling DNA/RNA, the next for the same trait but in another species’ XNA, with the XNA section being useless and “invisible” to our bodies and vice versa for the aliens’). Could this sort of thing reasonably exist within a species without having to be artificially made or installed, especially if specifically used or even evolutionarily selected for this information-sharing function? (E.g. perhaps initially the species has the basic property of those multiple genetic material types but not the function of coding a shared trait multiple times across different types, until that behavior is selected/bred for)

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  • $\begingroup$ Way to make this work (or at least, make it less impossible to suspend disbelief): Some ancient alien intentionally sent out 'life bootstrapping packages' that cause life across the universe to share far greater similarity. $\endgroup$ Jun 19, 2023 at 15:56

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It doesn't seem plausible.

There's a lot to unpack about why you can't do this with genetics, but it boils down to a common misconception. DNA doesn't code for "traits". DNA codes for proteins, which may cause certain traits when the rest of the body context is taken into account.

Let's take MC1R for a simple example, one of the key genes that determines your hair color. Specifically, it codes for the protein melanocortin 1 receptor, which is taken up by melanocysts that make pigments. If melanocortin 1 receptor is present, they make eumelanin which produces brownish hair. If it's not present, the melanocysts make pheomelanin which produces reddish hair.

It's tempting at this point to say that MC1R codes for brown hair, but this is due entirely to the melanocysts and how they respond to melanocortin 1 receptor. If you inserted that gene into another organism, it might have wildly different effects. If an animal's melanocysts (which are themselves made of proteins coded for by other genes) function differently, MC1R might provoke the opposite change, causing pheomelanin and suppressing eumelanin. It might cause the melanocyst to create another pigment, or stop working altogether. It might have no effect at all.

So the short answer is, no, an animal could not produce genetic code that expresses the same trait in different chemical bases. It can't even produce code that expresses the same trait in the same chemical base, but in different species*. It can't produce code that expresses the same trait in another species that it does in its own species, because genetic code doesn't code for traits, only proteins - and the effects of those proteins depend on the whole biochemical context.

*There is a caveat here, which is that related species often (but not always!) have related biochemistry too. To continue the earlier example, most mammals' melanocysts are probably pretty similar, and if you tried it, you would probably see most of them respond to MC1R in a way that's not too dissimilar to humans. But that's because we share a common ancestor with those species; it's not something you would expect to work between aliens.

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It depends?

If you want to have a "universal donor" that can influence genetic information of species developed on other planets you can forget about it. Even if they all use same 4 nucleotides of DNA.

The issue here is that DNA is a sequence that encode mRNA (and has control "circuits" around coding sequences). Unless you have closely related organisms same DNA sequence won't transcribe in the same mRNA (there are differences even on our planet - as RNA sequence is processed and cut; and here all living beings most likely share a common ancestor). Not to mention control mechanisms that guide gene expression won't work the same way. The next issue is translating that mRNA into proteins. Even a minor change in the process will result in a different protein. And here we again ignore post-translatic modification of proteins, which result in a different results on Earth in relatively closely related organisms (we cannot even use insect cell cultures for many human proteins, and insects are very close to us evolutionary speaking; way closer than any alien). And finaly: even if you got the exact same protein into the host cells, it still wouldn't work! Proteins need the proper environment to work correctly. And that includes all the other proteins in the cell. It would be like putting a gear shitf mechanism from a car into a 17th century sail-ship. It wouldn't really do anything.

But not all is lost! Your suggested mechanism could work if it were limited to a single biome - life originating from a common ancestor. It doesn't even need to be limited to one planet if someone were to spread that life off-world. If your mechanism were to give all life on your planet an evolutionary advantage then it could theoretically evolve.

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We already have something like this! On Earth, we call it...

a virus.

Our leading theories right now suggest that humans and other animals have all kinds of stuff in our genetic code that wasn't put there "naturally," but is rather the result of viral infections tinkering with our genetic code. There's absolutely no reason to believe that a species on another planet couldn't likewise be susceptible.

There is a catch, though. For the most part, the genetic information this virus passes on is "junk," garbage genetic code that as far as we can tell, doesn't do anything, good bad or otherwise. It's like opening up a text file, typing in some random letters, and expecting it to still make sense. This is where I see a connection to your XNA example; viruses already pass on genetic information that is going to be meaningless to most hosts.

How to make this "useful" instead of a "one or two actual changes in a million years" sort of functionality is up to you, but the base capability isn't a stretch.

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Forget about whether it would work in the "real world", and also forget going into enormous detail. Just write your story and let willing suspension of disbelief do the heavy lifting.

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    $\begingroup$ I mean I could do that, but I already knew I could. And maybe I WILL do that, but I’d still like to first see if there’s any sort of solution or hypothetical science idea I can use to at least form a general, very basic explanation out of, even if it’s just a concept to point in the general direction of when questioned. $\endgroup$
    – inkwell87
    Jun 18, 2023 at 23:51
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If you had nanobots that were capable of synthesizing arbitrary small molecules and splicing these together in whatever format was desired...

And if those nanobots stored both information on say, DNA and another alien genetic molecule...

Presumably these nanobots could then alter the genetic code of both DNA, and the alien genetic molecule. The instructions for carrying out these modifications would have to be stored in the nanobot, itself very small, so data storage capacity is very limited.

I expect you'd need some sort of hand-wavium picotechnology to be able to do this. Perhaps the data is stored in quantum foam, or is external and accessible via some not-so-easily-decohering entangled particle inside the nanobot (this doesn't work, entanglement almost certainly can't be used to transfer information, even subluminally, it's called the "no cloning theorem").

Given good software, the nanobot isn't limited to just two such genetic molecule systems. Probably, the thing is limited only by whatever principle it uses to do chemical synthesis/modification (some molecules may be impossible to synthesize way down low in its energy regime).

Whether this could arise naturally, who the hell knows? I can't even tell you with certainty that Earth biological life could arise naturally. I'm not big on intelligent design, but there are no witnesses and we've not been able to replicate the experiment.

I'm assuming you mean for this system to arise in an unintelligent manner (akin to the traditional idea of evolution). It's pretty clear that if our biology arose in that same manner, that there were quite a few things that seem exceedingly improbable, yet those happened. I take this to mean that nearly any improbable material system might also arise, supposing it does not violate physics/chemistry themselves. Supposing, of course, there is an evolutionary pressure for such a thing to come into being.

No clue what that would be those, hopefully your story provides ideas for that.

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