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In this world, time travel is possible, but the only thing that can be sent back in time are thoughts. From the perspective of your past self, you suddenly one moment realize that you have "memories from the future" -- more precisely, a knowledge of "what if", and more "wisdom" since you're spiritually suddenly older.

Given that you have different knowledge than you would if you didn't send your memories back in time, that without a doubt means that you would do things differently, at least slightly. You cannot mimic the precise way you did things before because you're concious about it. The moment you receive memories from the future, a new "timeline" is spawned, because the butterfly effect undoubtly propagates from your different decisions/actions, meaning that the future won't be precisely the same as you remember it, and it will just keep diverging more and more as the time progresses.

In this chaotic interpretation of the world, where even the slightest change in its structure is bound to propagate into a completely different outcome, how does that affect genetics?

My actions can make a couple have sex a few minutes/hours/days earlier/later, but would the result be the "same" child? The unpredictable nature of this world means that the child won't grown in the same enviornment, so he will (probably) grow up into a completely different person from the psychological point of view, but what about his genes?

Would a person's genetic signature be exactly the same if he was concieved at a different point in time, from the same parents?

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    $\begingroup$ Do two children born to the same parents, at different times (so, non-twins), have the same DNA? $\endgroup$ – VLAZ Aug 26 at 9:45
  • $\begingroup$ @VLAZ That's why I was asking about minutes/hours apart. You can't have non-twins with less than 9 months between them. I was 99% sure that the answer would be "no", but thought that maybe it's not that clear since I don't know anything about genetics (eg. maybe all of the sperms from the same ejaculation carry the same DNA, etc). $\endgroup$ – Lazar Ljubenović Aug 26 at 10:56
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Generally, no

It's a pretty common trope that time travel fiction loves, the whole 'kids are the same' thing. Occasionally they'll drop a line like 'the timeline stays the same' to justify it. But you are correct. Transferring a conscious back in time will lead to minute differences due to the butterfly effect - even more if said time traveler went back to change things. Considering that there can be around 300,000,000 sperm per drop of semen, any change to the Brownian motion can affect what sperm enters the egg. And there are 8,388,608 different chromosomes variations in sperm, not counting crossing over between chromosomes, so they'll each be different.

The egg is a bit easier to get the same, due to the fact that human females generally only have one at a time. If, for instance, you time travel to the day of conception, it will be the same egg. However, if you time travel a year beforehand, again due to the butterfly effect, a different egg is picked.

However, no amount of time travel will allow to get genes that the parents do not have. The genetic signature, as you put it, will not be the same, but will be recognizable siblings.

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You're basically asking if fraternal twins and identical twins are the same thing. Fraternal twins are siblings conceived from two eggs and two sperm at the same time. They are no more closely related, on average, than any other siblings. Identical twins are formed from one egg and one sperm that, shortly after conception splits into two embryos. These embryos develop into identical twins; to the naked eye they may be indistinguishable. A DNA test can tell them apart, because once they split they'll start accruing different mutations, like we all do, but they will be extremely minor changes.

Your time traveler, and his alternate self are essentially just siblings, or at most fraternal twins.

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    $\begingroup$ I don't think that is quite correct for time delays varying between milliseconds and days. Fertilization will occur with a different sperm but the same egg.So genetic similarity between alternate self will be 75%, less than the 100% for identical twins, but more than the 50% for normal siblings. For longer time delays, there will be a different egg, and then normal siblings will be the result. $\endgroup$ – Penguino Aug 25 at 22:39
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    $\begingroup$ @Penguino Possibly. But do we know that the order the eggs are released in will always be the same? Just because the date is the same doesn't necessarily mean it must be the same egg. $\endgroup$ – Ryan_L Aug 25 at 22:59
  • $\begingroup$ yes that is a valid issue. My comment is valid if, not only is the delay/advance in fertilization only for a few days, but also the 'cause' of the delay is also only a few days earlier. If that is the case the egg's release will already have happened or will already be in process. $\endgroup$ – Penguino Aug 25 at 23:45
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Genetically speaking you receive 50% of your genes from you dad's sperm, and the other 50% from your mom's egg. The important thing here is for the egg and sperm to have the EXACT same genetic code - no differences. Now, I'm not sure if multiple eggs/sperms could contain the exact same randomized set of code from your respective parent, will edit after some research, but if this is not the case, the baby conceived must have the EXACT SAME sperm and egg.

Here's where time and stuff will play a role. If your mom conceives 1 month here or there away, it won't be the same egg. If the same sperm doesn't come out of your dad, and the same sperm doesn't 'win the race', again, not the same baby.

Note about twins: Identical twins have the exact same code, but fraternal twins do not. All of the aforementioned issues still apply. Again, if we account for this variable, it adds to the complexity of your question too.

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