If Star Trek transporters actually existed...

Bob and Dave transport down to Earth from their ship. But something goes wrong and their DNA is swapped over! Not their cells as such, just the DNA strands within each cell.

What would happen to them in the ensuing seconds, hours and days?

I can imagine a few ways it could go:

  1. Rapid, gradual degradation in most organs (deeply unpleasant, would perhaps be similar to extreme radiation exposure). They might survive a few days perhaps.
  2. No immediate symptoms, but perhaps their appearance slowly changes over time as cells are replaced - maybe they'll end up looking like eachother.
  3. Catastrophic brain failure within seconds.

I think the first one is most likely. Perhaps the body would consider the altered DNA as simply a very severely mutated mess. Would the body reject all of its own cells at the same time?

What would really happen?

  • $\begingroup$ For future reference, please note that the help center forbids you listing your own answers and asking for more. We allow it only when you explain in detail why any answer you posit won't work for you, so they become restrictions to the question. $\endgroup$
    – JBH
    Aug 16, 2023 at 19:29
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    $\begingroup$ They were not intended to be my answers, because I don't have any supporting evidence for them. Also other SE sites demand some evidence of forethought or research on the topic at hand. Good to know though, thank you. $\endgroup$
    – Wossname
    Aug 16, 2023 at 20:32
  • $\begingroup$ Just to make sure -- you are aware of Cronenberg's Fly? $\endgroup$ Aug 17, 2023 at 14:54
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    $\begingroup$ @Peter-ReinstateMonica, Very much so. It appears that inter-species DNA swapping is somewhat inadvisable, without proper precautions. $\endgroup$
    – Wossname
    Aug 17, 2023 at 15:01
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    $\begingroup$ @JBH a querent including examples of what they think may happen in a given scenario does not even come close to the help-centre example of “I use ______ for ______, what do you use?” $\endgroup$
    – M S
    Aug 17, 2023 at 15:39

4 Answers 4


The immediate problem I can see is the antigenic reaction of the body: as soon as non-self surface proteins get exposed by the cells produced with the new DNA, the immune system will start attacking them, more or less like in an organ transplant without immunosuppression.

This would as a consequence lead to rapid death, but not within seconds. I would say it would happen in hours, and would get worse the more new cells are produced.

The time scale would be comparable with acute radiation poisoning, with the difference that there the body fails because no new cells are replacing the dead ones, while here new cells are produced and attacked by the immune system.

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    $\begingroup$ worse at first the original immune system is attacking new cells but then as the original immune cells get used up, many immune cells have a fast turnover, eventually the new immune system starts attacking everything that is left including the long lived cells so things like neurons and bone cells. $\endgroup$
    – John
    Aug 16, 2023 at 13:45
  • $\begingroup$ I think it'd be even more like acute radiation poisoning: any cells that were actively in the process of dividing or transcribing genes from their DNA would likely end up with severe damage, and the swap would have drastic effects on all the regulatory machinery that gets all mixed up with the DNA itself code...the histones, chaperone proteins, transcription factors, etc. I rather doubt the immune system cells will be in any condition to attack anything...if they even retain their identity as immune system cells. $\endgroup$ Aug 17, 2023 at 0:24
  • $\begingroup$ @john and heart muscle cells which almost never divide after early childhood (which is why primary heart cancer is so extremely rare) $\endgroup$
    – Tristan
    Aug 17, 2023 at 13:35
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    $\begingroup$ I think the time-scale would actually be quite rapid. The main problem wouldn't be the cells being killed, but the immune reaction itself. As the immune system starts seeing foreign antigens everywhere, it would quickly go into overdrive, causing massive inflammation, high fever and possibly even anaphylaxis. $\endgroup$ Aug 17, 2023 at 15:54
  • $\begingroup$ @John New immune system won't attack what is left. The adaptive immune system "trains" the newly born immune cells to not recognize anything already present in the body. So if you somehow skipped the initial immune reaction, the newly born immune cells will likely not attack the old cells. $\endgroup$ Aug 17, 2023 at 15:55

Another answer addresses a valid point: if person A and B switch DNA, person A's immune system will recognize new cells or antigens produced with person B's DNA as foreign and attack them. I agree that this is the most obvious cause of death. However, this might not necessarily result in death due to an important consideration: the antibodies on the surface of cells, immune and otherwise, are produced from instructions in DNA.

This would mean that as soon as person A and person B switched DNA, person A's immune cells would begin producing person B's antibodies and person A's other cells would begin producing person B's antigens. Even long-lived cells like neurons actively recycle cell-surface proteins. Because of this, assuming a person can survive long enough for their cell-surface proteins to be replaced, there's no immediate reason they would die.

Furthermore, in many situations, immune antibodies are "used up" once they bind to a foreign antigen, and many immune cells have a turnover measured in days, and this is shorter if they're fighting an infection. This would be even faster given new immune cells made with person B's DNA possessing person B's antibodies would be actively attacking person A's old immune cells possessing person A's antigens. If someone can survive the initial allergic reaction and doesn't develop an autoimmune reaction to their new antigens during this period, they may not immediately die.

However, as another answer points out, DNA is very interconnected to the rest of the body. Which proteins are being transcribed from the same sequence of DNA varies from cell to cell even in the same body due to epigenetics. If the transporter is merely randomly swapping chromosomes, this could lead to death. For instance, since every cell in the body has the instructions for how to make stomach acid, if person A's heart suddenly gets DNA actively transcribing proteins to help digest food, that could be fatal. Person A and B have different numbers of cells and different numbers of each cell type, and epigenetics in their brains are important for memory and personality. Even if the transporter attempted an approximate cell type-to-cell type chromosome swap (liver to liver, skin to skin, etc.), this could result in cognitive deficits, massive metabolic dysregulation, and down the road, cancer.

On the other hand, thinking optimistically, we can also assume the transporter is aware what DNA is and how epigenetic regulation works. In this case, since most humans have the same genes, just different versions of each gene, the transporter could simply set the level of transcription of person B's genes to the same level those same genes (just different versions) were previously being transcribed in person A's cells. In this case, if person A survives the initial immune response, they may be able to live on indefinitely, just with diffuse and unpredictable changes. For instance, their earwax may go from wet to dry. Regardless, they would probably suffer from obscure illnesses due to cells growing in a scaffold (body) made using different instructions than those they contain--maybe person B's DNA for blood filtration assumes a certain kidney structure.

In sum, it really depends on how exactly the transporter is swapping DNA and how bad the initial immune response is.

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    $\begingroup$ Yeah, it's called "cancer", +1. $\endgroup$
    – Mazura
    Aug 17, 2023 at 1:11
  • $\begingroup$ Excellent points, +1. I still believe the initial reaction would be too severe to survive. Recycling of surface proteins takes at least hours or days, and there's no way a person could survive a runaway immune reaction against all cells in their body that long. They might have a chance if they were prepared for the swap with immune-suppression drugs like those given to organ transplant patients. $\endgroup$
    – Cloudberry
    Aug 19, 2023 at 7:36
  • $\begingroup$ You get close to this with your idea of swapping between like tissue types, but a more fundamental problem that there isn't a one-to-one correspondence between cells of two different individuals. Even with some mechanism for finding "similar enough" cells to swap, you'll have many cases where there isn't a matching cell in the other body to exchange DNA with. So does that DNA just end up splatting on the floor while the cells it came from end up empty? $\endgroup$ Sep 24, 2023 at 0:25

It's probably less destructive than you'd think.

There are human chimera, who have multiple sets of DNA in the cells that make up their body, typically from before they were born. (This is sometimes referred as being mosaic. This can lead to the tissues of the body effectively being created from different genetics. Bob and Dave start with exclusively one set (probably) but will probably develop tissues with the other set (for example, people with bone marrow donations have blood and seminal fluid which is genetically the donors).

Whilst there are undoubtably potential problems with immune system interactions (perhaps this is why chimerism is so rare -- if there is an incompatibility, the child does not survive to be born), we have present-day technologies that can stop the immune system before they can fix the transporters to turn them back.


Edit: The OP has disagreed with my premise (you can't swap DNA) because his/her transporter can move atoms at the atomic level. The OP has completely missed the point of my answer. DNA can't be swapped. Not because the OP hasn't the technology to do it, but because Mother Nature doesn't care if he/she does. Now that you understand that when I state "DNA can't be swapped" it's NOT relative to the OP's technology, read on.

You're not thinking about the interconnected nature of DNA

DNA isn't something that exists independent of the rest of the body. In other words, you can't "swap DNA" between two bodies.

Every cell in the body exists because of the DNA. The DNA has replicated throughout the body because of the DNA. The construction plans and operational plans of the body cannot be separated from the body. If they could, the result would be instant death. It would be like taking an operating system that was not designed to be self-aware of the possibility of transplant from one computer and overwriting another, arbitrary computer's operating system with it. Let's use Windows 95 as an example. The result? Dead computers that must have the operating system re-installed. How do I know this? I once tried to update my computer by moving the hard drive from the old computer to the new one and turning the power on. It was a heaven-shaking mistake....

What would appear on the transporter pad is the other body, which was designed and operated by that body's DNA.

Therefore, the real question is: is it possible to transfer the synaptic/brain structure between two bodies?

You used the tag, so the answer is no. You might, maybe, swap two patterns between twins. Maybe (at least that one meets my sense of suspension of disbelief), but arbitrarily between two people? No. The result would be irrecoverable brain damage that would have an all-too-likely chance of killing the body.

However, that hasn't stopped SciFi from writing about it. If you can stomach the era's misogyny, watch Star Trek TOS' final episode, "Turnabout Intruder." What's regrettable is that had the writers avoided the misogyny, it would have been a great episode about ambition, glass ceilings, and obsession. Oh, well.

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    $\begingroup$ "you can't 'swap DNA' between two bodies" -- Sure I can, my (admittedly malfunctioning) transporter can put arbitrary atoms anywhere it likes. :) $\endgroup$
    – Wossname
    Aug 16, 2023 at 20:36
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    $\begingroup$ @JBH what if OP had said "chromossomes" instead of DNA? $\endgroup$ Aug 16, 2023 at 23:41
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    $\begingroup$ I once tried to update my computer by moving the hard drive from the old computer to the new one and turning the power on. - Except you can do that, especially with modern OSes. Even in the Win95 days most hardware would be compatible with a standard set of lower-level drivers. Otherwise, you'd have a hard time installing the OS in the first place, or being able to install other hardware components. $\endgroup$ Aug 17, 2023 at 0:16
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    $\begingroup$ @JBH You keep agreeing that "it can swap X and Y" immediately followed with "X and Y can't be swapped" without actually addressing the contradiction. Is there some other condition you think needs to be met for it to "count"? If so, that should not only be stated as an assumption, it should be your answer. $\endgroup$ Aug 17, 2023 at 3:13
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    $\begingroup$ @JBH "It can swap tooth plaque for brain cells and foot calluses for lung tissue" and were the question about what would happen if that occurred, the answer would be "they die very quickly". "But they can't be swapped, either" of course they can. It's honestly insane reading this answer and subsequent comment in which you entirely (and quite rudely) reject the OP's premise based on nothing other than "it wouldn't be useful". Of course it wouldn't be useful, a quarter of the question is asking about how the person would die. $\endgroup$
    – M S
    Aug 17, 2023 at 15:45

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