I’m sure we’re all familiar with a time travel story where some guy travels back in time and through whatever plot device is utilized, becomes his own grandfather. Or maybe great-grandfather.
Now he’s returned to 2018 and submits to a comprehensive DNA test. Will there be anything there that’s going to make a geneticist studying the results ask WTF? Would the doc see any real indicators that the subject was playing fast and loose with the time line?
Specifically, would there be proof that he was his own grandfather?
I guess it depends on what theory of time travel you’re working under. If it’s a multiverse kind, then the time traveler’s own DNA doesn’t change, but there might be something in the “new” version of the time traveler that’s created in the new timeline, since his one set of grandparents are now closely related.
If it’s the single-universe kind, then you can run into a problem. Futurama did an episode like this where Fry becomes his father’s father. So the question there is: where did Fry’s Y chromosome come from? Fry inherited it from his father, but his father inherited it from him. There may be others like this as well, eternally passed between Fry and his father, but you could argue that they came from Fry’s grandmother or mother instead. So Fry’s Y may be unique in a detectable way.
I’d expect that the traveler would be homozygous to a greater than normal degree, but it might be mistaken for some other form of incest. I haven’t worked out all of the calculations, but I imagine that someone who was es own grandparent would look a lot like the result of a brother-sister pairing, genetically.
If you were your own grandparent, that means you have 100% matching genes. So from your grandparents to your parents and then to you, you’d have to retain a 100% match, meaning the “outsider” genes would have to also match, which would be a heaping amount of coincidence
