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I have in my series a group called "Chimeras". They were once normal humans but were exposed to an artificial gene-editing retrovirus known as the "chimera virus".

The chimera virus is a synthetic virus that lacks genetic information of its own and serves as a vessel for introducing foreign genes to the cells of a host. Every batch/strain starts as a blank slate, but copies the first genome they're exposed to for spreading to all future hosts. In a controlled environment, the DNA fed to them is carefully selected for desired purposes. Should they get into an organism without prior treatment, or if DNA is added to them irresponsibly, they end up carrying a sizable portion of genetic information to spread to all future hosts.

Any strain carrying foreign DNA works its way through the host, spreading across the majority of their cells and stimulating growth. Physical changes start slow and minor at first, but given enough time and nutrients, their body becomes unrecognizable and inhuman.

In trying to keep it somewhat grounded, there are some specifics on how the chimera virus operates.

  • It's not a fast process: A complete mutation into a chimera takes a lot of time and food for their body to grow and build any new structures/components. Their appetite massively ramps up for a while to gain the necessary material. It's not an experience most would willingly undergo, as the process is very painful. Think less Ninja Turtles, more "The Fly" in terms of transformations.

  • It's not "Lego-genetics": There are no mix-and-match parts here. Someone who received lobster DNA or something isn't just gonna grow a claw, the rest of their body is going to slowly and painfully warp too. No major change can occur in isolation, it always results in the rest of them changing to some degree as well. Having the chimera virus carry majorly different DNA strands at once (like say, a crab and a gorilla) will always result in the host dying. The species are simply too different, and the incompatible simultaneous changes to their body would not be good for things like.... living.

I know this is likely beyond modern (and probably all future) gene-editing technology, but does it at least make some degree of sense?

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  • $\begingroup$ contradiction: "virus that lacks genetic information" "vessel for introducing foreign genes". Restated: This document lacks instructions, it is a document to instruct... $\endgroup$ – Gault Drakkor Apr 7 at 22:24
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    $\begingroup$ It is extremely unlikely to happen if the virus is used on adults unless the virus can somehow stimulate a lot of other processes in the body, but that would lead to many other possible problems. If a fetus is exposed to the virus, the outcome will be different, but it is hard to say whether the resulting chimaera will be compatible with the mother's organism (if not you will get a miscarriage at best) or able to survive after birth. It might be better to handwave this rather than look for a scientific explanation. $\endgroup$ – Otkin Apr 7 at 22:29
  • $\begingroup$ Oh most definitely. The second generation of chimeras (who've been this way from conception) generally are better "put together " if that makes sense. There traits are mixed a bit more smoothly, so they have a lower rate of deformity and health problems. $\endgroup$ – Hammondverse Apr 7 at 23:12
  • $\begingroup$ You are not trying to create a scientifically plausible furry world, do you? $\endgroup$ – Philipp Apr 8 at 8:31
  • $\begingroup$ Some nitpicks about the viral aspect of the "virus". What you are describing as a way to introduce foreign genes is a "vector". Vectors can be of viral origin, but a virus MUST contain genetic material, otherwise it's not a virus. Hence you cannot have a "blank" virus with no genetic material. Additionally, viruses have no way to "copy" genetic material, they rely completely on apparatus of the host cells, the virus itself has no means to alter, replicate or synthesize anything. Real life vectors are created in a lab, by injecting needed genetic material into an empty virus shell. $\endgroup$ – JANXOL Apr 8 at 9:03
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Say you have an RNA virus, with genetic information to do the virus things. This is an essential starting point.

Virus that copies random.

The virus is modified such that the next generation of virus will also contain some random stretch of RNA from the host. Additionally the extra RNA will then also be included in the 'execute' upon infection.

So each virus will essentially each virus will have the virus payload plus some random RNA. With this every virus will have unique payload.

Problems:

  • The capsule of the virus may be to small to contain that extra RNA.
  • The viruses will be sub optimal, and over time will likely optimize away the function of including extra RNA. the extra RNA means much less virus output.
  • The payload is utterly random. So production of infected cells will be virus plus some random protein, which will interfere with the virus to replicate.
  • Will not do as question intends.

Virus set to insert preprogrammed.

The virus is modified to insert a specific payload

  • Will not do as question intends.
  • Most viruses will not have enough room to have more then a small payload.
  • The virus will likely optimize out the payload over time.

Overall problems

I really believe you are drastically underestimating how much information is needed to encode your chimera whichever it is. The structures, how to build the structures, how, where to attach the structures, the timing signalling.

You need to have the genetic information of the virus with the virus because if it doesn't. The virus can't replicate. It could infect at most one cell.

Random genetic information from one source put into another is almost guaranteed to do nothing of interest.

Chimeras will have to be engineered/created deliberately.

Possible solution Bacteria or fungus

Better option is to modify a yeast or bacteria to be the factories that produces viral like infectious particles that have the desired modifications. The bacteria or yeast do have enough space to have which ever chimera. But then there is a target to kill once enough chimera production has happened.

Some real world examples

This youtube video spider silk yeast . Describes part of a persons quest to produce spider silk. Breakdown of how the pfizer vaccine is arranged.

Conclusion

It can be done, just not the way you imagine. It would take immense engineering and research effort to create each viable chimera. ie if you want nekomimi (cat eared people). That's a decade or eight of work by a team.

Of course if you want a magic system that makes it so. then this all can be ignored.

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CRISPR-CAS!

CRISPR-CAS 9 is closest what you seek. Here it is in a overview:

Bacteria have a very rudimentary immune system. If they somehow repell an attack from a virus, they keep a bit of the DNA of the virus. This is placed in a special enzyme. If the enzyme encounters an identical DNA sequence it'll cut it out and replace with garbage DNA. The DNA of the virus now doesn't make sense and it'll not be able to use the Bacterium as a virus factory, killing the Bacterium in the process.

CRISPR-CAS 9 is a technique that can use this to it's advantage. The technology is still in it's infancy, but promises cheap, specific and mass produced DNA changes.

The technique will analyse the DNA. Spot somewhere you want to change. For example, hair colour. You check the exact DNA sequences that causes the hair colour for this individual. You check what sequences are needed for the desired colour. For each sequence you make an enzyme. Add the one sequence to the enzyme for targeted cutting and replace the garbage DNA with the desired sequence. Add enough enzymes over time to a body to change all DNA in the body.

So for each thing you want to change you need to know what DNA sequence or sequences cause it and for each you make a targeted enzyme.

I'm not an expert on this subject, but it's likely that some immune systems see the enzyme as foreign and will try to remove/neutralise it. In addition, it might be easier to target a few cells like a virus does, high jack their enzyme producing capabilities and let them build the enzymes for the duration they live. This might be enough in time and volume to change the whole body.

Also keep in mind that some things cannot be changed, unless you start triggering them with hormones and such. As you say a hand will not suddenly grow into a claw. That likely requires intermediate DNA sequences and hormonal changes for the right triggers of gene expression. Otherwise it'll be utter chaos and mass cell death, as the required enzymes and such that the cell normally makes with RNA don't match. An example. You change the DNA of a human to a lobster. The enzymes of the cells change. Unfortunately this governs a lot, like energy production, mitosis, markers for a thousand little activities that are now different. The cell and DNA don't match anymore, making the cell shut down or kill itself. You won't even have a chance to start the process of changing the cells for the new ones.

So your idea isn't outlandish. Something close to your idea exists. Although it promises the world, the technology is still in it's infancy. It might not be as feasible in the long run. We don't fully understand the human genome yet and the repercussions of changing a tiny bit of DNA, so promises is the most it can do right now.

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  • $\begingroup$ Yeah, I am aware of CRISPR, that was a pretty big part of my inspiration in making this. Of course, the extent of modification is probably beyond realistic levels, but that's where the general idea came from. $\endgroup$ – Hammondverse Apr 8 at 12:24
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I haven't looked into this scientifically, but if the virus infected the human's RNA it might be possible for the RNA to take aspects of the DNA of other creatures it's encountered (as long as it's had contact with said DNA) and mutate. I'm not sure how likely it will be that the human will grow a scaly tail, but it probably could affect the already-existing cells and, for example, change the amount of melanin in the person's skin or add an amino acid that could make the skin thicker, etc.

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IANAB (I am not a biologist)

Think of your DNA as doing 3 things

1. Instructions to build

Your genes encode instructions to build your body - but they're not blueprints. Rather, they're like a step-by-step recipe, or a series of instructions. (Not really even like that, but it's a good way to think about it.) You're getting from one end of the room to the other, not with a map, but by instructions on how long each step should be and which way to turn when you encounter an obstacle. Or like applying a succession of folds to a piece of paper to achieve a piece of origami.

Genes don't know, beyond basic "if this happens, do this", where they are in the room or the paper folding. DNA doesn't know what the end goal is. So the instructions which would cause an undifferentiated lump of lobster stem-cells to become a lobster claw wouldn't make a hand become a lobster claw. At best, it could make lobster claws erupt like pimples from your knuckles (or brainstem!) - and probably not that.

2. Instructions to keep things running (and when to stop)

(Note that we're grouping instructions for convenience of thinking about them; individual cells executing their DNA have no notion of which kind of instructions they're following.)

When cells don't stop multiplying (but they should have) you get cancer, which can kill you. When cells don't know how to keep doing what they ought to be doing, you can easily die of that, as well.

If a human's maintenance instructions are replaced with maintenance instructions which make sense for a lobster, but not for a human - you'll end up with some combination of cancer and cellular or organ failure. That is, you'll just die.

  1. Instructions to fix broken things

Your body's systems, and to some extent presumably your actual DNA instructions, do things differently when there's a sign that something has gone wrong. Blood, normally meant to flow, clots up when there's evidence it's leaking out of the body. (If blood clots and shouldn't, you can die of that, too!) Singed or otherwise damaged tissues may kick into self-repair overdrive, demanding extra resources and turning up their rate of division until the evidence of damage has faded (and if it doesn't, fever, cancer-like behavior... you could die).

Introducing new DNA instructions to a mature, or mostly-mature organism is going to run into problems.

The instructions to build a lobster from one or a few lobster cells will not make sense in the context of an already-grown organism. It takes an aware third-party to look at your hand, identify it as something similar to a lobster's claw, and to try to replace the hand with a claw. The skin cells, muscle cells, etc, in our fingers don't know whether they're in our fingers, or toes, or somewhere else. And even if they did, like origami, a series of instructions on how to fold a new sheet of paper just wouldn't apply to an already-folded sheet.

The instructions to keep a lobster alive, or fix damaged parts of a lobster, also wouldn't work on a human. In the same way building maintenance instructions for a skyscraper would be at best meaningless, and more likely would be destructive, if applied to thatched cottage, and vice versa.

"Mutation" of an adult organism to resemble another adult organism, simply using the DNA from the second organism, is a fantasy which does not make sense. It can be a fun or interesting fantasy, but it is not science-based.

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  • $\begingroup$ Not the most important point, but I just want to clarify. I used "lobster" as an example since it's not a species I plan on using, and I wasn't attempting to connect this back to a specific chimera. For the most part, I've limited the hybridizations to tetrapods. $\endgroup$ – Hammondverse Apr 9 at 15:13
  • $\begingroup$ @Hammondverse I just ran with the example you gave because it was simpler to talk about a specific thing. The same argument would apply to jellyfish and spiders, or whatever pair you can think of. (Chimps and humans might be close enough that it wouldn't be lethal, but in general... Though even that's assuming you were replacing blood-clotting instructions with blood-clotting instructions, and not blood-clotting instructions with finger-growing instructions.) $\endgroup$ – Jedediah Apr 9 at 15:17

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