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I watch the TV show The Last Man on Earth and there is only a handful of women and men living. In the show the few are trying to conceive. They haven't covered how eventually they will have to inbreed a generation or 2 away.

In the event that mankind is wiped out to a handful of people and not enough for genetic diversity could the amount of people needed to repopulate the Earth be reduced by using Gene Editing and Modification?

Although several people survives in remote parts of the world only a few had good DNA, age and disease free to procreate.

With the help of a geneticists and a salvaged lab could DNA be modified to have your siblings baby but healthy?

As science progresses the plausibility of Adam and Eve giving rise to a whole world sounds more and more realistic to me. Can humans be so genetically perfect not to have defect for many generations?

What is the minimum human population necessary for a sustainable colony?

Muze
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  • Minimum Viable Population is what you're looking for, – RonJohn Mar 22 '18 at 21:46
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    It is one thing to fix known genetic defects, replacing them with known "good" copy of DNA fragment. It is another to introduce random mutations just to create diversity. Which one are you asking about? – Alexander Mar 22 '18 at 22:00
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    "There will not be enough people for a gene pool to repopulate." The MVP for humans is less than 4200 people. If there aren't that many people, there's no hope of them running a DNA lab while struggling to survive. – RonJohn Mar 22 '18 at 22:01
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    If you are going to ask whether something can be done in such a vague manner, you should first ask yourself why it would not be possible. – The Square-Cube Law Mar 22 '18 at 22:10
  • Way better to alter the genes and then implant it, rather than trying to make it "automatic". We still don't know how will the GMOs react over several generations (with more advanced organisms) and most GMOs are made infertile on purpose. – Nuloen The Seeker Mar 22 '18 at 22:11
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    The mvp does not apply if there are no negative recursive traits in your population... – Pliny Mar 22 '18 at 23:00
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    "With no electricity DNA spoils" That's not how DNA works. – RonJohn Mar 23 '18 at 03:55
  • "Could negative traits be mitigated through DNA manipulation" maybe at some unspecified time in the future, and if the only 12 survivors happened to be a few men and nine women who just all happened to be geneticist doctors and lab technicians who also happened to be electricians and plumbers, in a laboratory with years of diesel fuel to power the generators needed to run the facility. Bottom line: the reality-check answer is no. – RonJohn Mar 23 '18 at 05:01
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    @Muze I think that a technology that could replicate DNA of other people and then clone them or impregnate an egg with that DNA is a safer bet. Since the rest will be up to nature and the results could be monitored safely. While mutations caused by GM could be hard to monitor, since the side effects could be hidden for a few generations. It could also be safer to just not interfere and let nature decide who can survive. Several mutations can occur in early generations, but the surviving individuals will be distant enough to enrich the gene pool. (Some animal breeds were made this way) – Nuloen The Seeker Mar 23 '18 at 10:04
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    "It said able to conceive there could be more people." Twelve humans in their breeding years (which includes older men), and a lot of post-menopausal women. We keep telling us why your question is flawed, but you keep ignoring us. – RonJohn Mar 23 '18 at 10:15
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    A tip: I just had a look at your profile and it's kind of worrisome that you "hate being suspended or banned". I am not a mod and I don't see any reason to flag your stuff for a suspension, but please be aware that there are automatic question bans if you have too many closed questions and questions with a negative score - of which you have quite a few. Please take a look at What can I do when getting “We are no longer accepting questions/answers from this account”? and our Sandbox. – Secespitus Mar 23 '18 at 11:02
  • The answer is that such genetic modification tech doesn't exist just yet. So in your story your tech could be whatever you want it to be. So with that allowance, yes, in your story, you can genetically modify a siblings offspring to be ok. – Len Mar 24 '18 at 17:00
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    Muze, this is another one of your "I'm just curious" questions that has nothing to do with worldbuilding, so I voted to close it. If you disagree with me, please explain your world (and its technology) in detail so we can acctually answer the question. – JBH Mar 27 '18 at 08:12
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    Well, this is an oldie in the VTR queue. (1) I doubt there is scientific evidence that we can edit our genome in the way you need. I would not believe any answer that says "yes" if they don't link to scholarly articles proving the ability. (2) If we could edit the genome as you suggest, then it's not the parents that need the help, it's the offspring. You'd fix the child's deficiencies. That's very plausible in my book. (3) Or you could ignore the gene editing completely and inbreed like crazy. The healthy will live, the unhealthy won't, evolution is served. Nevertheless, VTR. Cheers. – JBH Jan 14 '19 at 22:08

3 Answers3

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Easier, More Effective Methods Available

Genetically modifying people to inbreed doesn't make much sense when there are better options on the table. The easiest we could do with today's technology is to freeze sperm and eggs so that you can artificially rejuvenate the gene pool periodically. On top of this, if the planet is smacked hard enough to kill off that many people basically the entire ecology of the planet is dead too so there really isn't any way for humans to survive or maintain a high level of technology anyways.

The Square-Cube Law
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TCAT117
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Inbreeding is only a problem if there are genetic diseases in the DNA. If you remove all traces of genetic disease then inbreeding isn't a problem (until new mutations cause new ones anyway).

That said, they'll be blown back to the stone age so a scientist's time would be better spent building a better bunker or spacecraft than building incest resistant people.......

Thorne
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The trouble with inbreeding is all about the fact that we have TWO copies of every gene; because we get one chromosome from each parent.

So; if you get a mutant allele that doesn't work from one parent, the chances are you won't even notice if you got a functional version from the other parent. This happens all the time.

When two people who are closely related have children, the chances of the child getting two bad copies of a gene increase very substantially, because both parents have a recent common ancestor who gave them their genes.

Also, the idea of 'genetic diseases' is not entirely correct. For any gene, there are thousands of alleles; each one might differ by only one nucleotide. Some are more or less functional but since the function of most proteins (proteins are encoded by genes) are very complex, each allele can be more functional in one situtaion and less functional in another

Consider the sickle cell gene; it makes a 'faulty hemoglobin protein' which aggregates at low oxygen tensions. But that same protein is protective against the malaria parasite (which lives inside red blood cells). So the same allele of hemoglobin is harmful (can't carry oxygen as well) but is protective against a very nasty disease for which there is no cure. Most alleles are like this; they have advantages and disadvantages.

Stephen D.
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