What would happen to a person if their DNA was swapped for someone elses?

Question

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?

Answer 1

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.

Answer 2

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.

Answer 3

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.

Answer 4

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.

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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 science-based 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.