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Discussion on the question Why were blood and hair follicles from 25 people put on the Moon? calls into question whether this is a stunt or might have any basis in science.

There's two parts to my question:

  1. If somehow preserved well, do hair follicles and blood samples from a group of humans provide sufficient coverage alone to reconstruct a human population as far as the DNA content is concerned? Ignoring that you don't have an egg to put it in, is enough DNA present, or would there be key bits of DNA missing that you'd need a germ line sample in order to get? I suppose this can be asked as "can we clone people from blood and hair follicles alone?"

  2. Would 25 individuals be enough to obtain a viable population of clones?


Background from the linked question:

The Wired.com article A Crashed Israeli Lunar Lander Spilled Tardigrades on the Moon says:

Spivack had planned to send DNA samples to the moon in future versions of the lunar library, not on this mission. But a few weeks before Spivack had to deliver the lunar library to the Israelis, however, he decided to include some DNA in the payload anyway. Ha and an engineer on Spivack’s team added a thin layer of epoxy resin between each layer of nickel, a synthetic equivalent of the fossilized tree resin that preserves ancient insects. Into the resin they tucked hair follicles and blood samples from Spivack and 24 others that he says represent a diverse genetic cross-section of human ancestry, in addition to some dehydrated tardigrades and samples from major holy sites, like the Bodhi tree in India. A few thousand extra dehydrated tardigrades were sprinkled onto tape that was attached to the lunar library.

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    $\begingroup$ If the 25 human samples were from diverse regions of the world, i'd bet that it would be easy to build a human population with medical supports, although the frailties may not make them viable for wild tribe life. $\endgroup$ – com.prehensible Aug 11 '19 at 8:48
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    $\begingroup$ No, because AFAIK you can't just clone a mammal from DNA. You need a mother from the same or a closely-related species. Think of it as "blueprints": instructions to a factory that has a lot of highly-specialized CNC machinery. Without having those machines (or being able to build duplicates), your CNC instructions are useless. $\endgroup$ – jamesqf Feb 8 at 3:50
  • $\begingroup$ @jamesqf so perhaps the use of the verb "clone" in the question was misguided. There's still the question of the fraction of the genome present in hair follicle and blood being sufficient. $\endgroup$ – uhoh Feb 8 at 4:01
  • $\begingroup$ If you had the technology to build a human from the DNA in hair follicles, you'd probably have the technology to synthesize DNA from scratch. So instead of sending up 25 hair follicles, send up an SSD with DNA sequences from thousands of people. $\endgroup$ – user137 Feb 13 at 13:35
  • $\begingroup$ @user137 a little bit like this? $\endgroup$ – uhoh Feb 13 at 13:39
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If we assume for a moment that the samples could be successfully cloned, 25 individuals is probably not enough to maintain a stable human population for more than a few hundred year without experiencing severe inbreeding depression and eventual extinction.

In population biology, there's a general rule of 50/500 for minimum viable population sizes. Essentially, a minimum population of 50 is needed to prevent inbreeding depression, and 500 to stabilize genetic drift. Of course that's a generalization used in management situations, and lots of factors go into making a calculation like this with any amount of precision.

One estimate gives a minimum viable human population (for generational space travel and permanent colonization) of ~40,000 humans in order to maintain genetic diversity. But that only applies to a population carefully screened and selected to maximize the effective population size. Another suggests 160 people could be enough for a stable population, as long as they return home to mix it up with the rest of humanity every 200 years or so.

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  • $\begingroup$ Thank you for your well-supported answer! I was worried about the samples not covering a complete genome, but didn't stop to think about this issue at all! $\endgroup$ – uhoh Feb 12 at 23:55

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