Space Colonization and Genetics

[infernovia]

So, quick question here. Let's say we have magically terraformed some planet and want to colonize it. We can cryogenically freeze people but not fertilized eggs, nor do we have the technology for artificial wombs. So my question is, what is the least number of people you can put in here without seriously incurring genetic defects?

Note that the most preferred way to colonize would probably be a shuttle of first generation adults along with artificial wombs and a large number of cryogenically frozen eggs.

[Rowadanr]

but... but we can already freeze eggs and sperm, what could possibly preclude that? The artificial wombs bit is somewhat more difficult, however, so will take that as a limiting factor. If you for some reason weren't able to carry a bank of eggs and sperm with you for fertility-clinic purposes (no artificial wombs needed, ivf would still create an addition to genetic diversity if used). And ignoring the fact that for a hundreds-of-years project like terraforming you'd probably want people there from the get-go unless you have willing AIs...
Going with the limits you've actually stated, I'd say about 50 people with a good range of genetic diversity. That's a manageably low number with little enough pressure for inbreeding down the line

[Izawwlgood]

I remember seeing a number somewhere, and I apologize how useless this post is for not remembering where or what it was. I imagine you are presupposing that they are never going to get another influx of humans, and will truly be the founders of a colony?
My impression is the number is smaller than we'd expect? Maybe 50-100? With careful pedigrees, you'd probably only suffer an elevated risk of inbreeding related abnormalities in the fourth or onward generations? If you got particularly unlucky with some of the founding members, it's be all the worse.
But just to point out, if IVF and freezing zygotes is an option, and terraforming is going on, I wager pretty complex genetic manipulation is also going to be a possibility.

[idobox]

Artificial wombs wouldn't be that useful.
There's no point in growing a lot of kids if you don't have enough adults to raise them. Female only settlers will be able to give birth to more kids than they can decently raise while also terraform/colonize a planet.

[infernovia]

Darn, I remember reading about how the population would be screwed if it went below 1000 or something. I remember being reference to the conservation of animals mathematics which states that we might be seriously under-estimating the population need, but it's not like we are forcibly selecting mates there. But yeah, there will be no additional humans sent there until wayyy later, I am working under the assumption that the human would attempt to attach this plan to as many planets as they possibly can.

As for the adults > kids, you have to remember that the cells are mostly to inject diversity into the system more than anything else. So you don't have to use them all at once, and even without the artificial womb, I don't think any girl wants to be a baby producing machine lol. Instead you can start using more and more of them in the latter generations. But yeah, at this point, there would be some serious progress in genetics research.

[WarDaft]

You'd think you'd need more people to establish a fully self sufficient colony than for genetic diversity. I mean, unless we're sending more people (which alleviates genetic concerns) this is the seed for an entire civilization. If you send 50 people, the stress on each person is going to be very high, and if one person dies, you've lost 2% of your culture, capabilities... what if a doctor dies? Practically everyone will be mission critical. You're going to want enough people to push the odds of mission failure due to loss of life or faculties or any other human fragility out to 6 standard deviations at least. Think about how much the mission to another planet would cost in the first place, now consider how many people end up with say, cancer. There are plenty of other things that can go wrong too. Add in that you're in an inherently hostile environment, and you're going to be sending a lot of people.

[Quizatzhaderac]

I think there would be huge difference in the numbers you'd need between an ideal breeding program and natural breeding. 50 might suffice in ideal conditions. In unideal breeding program you'd have people dying before reproduction, being infertile, copulating outside of the program. Without a program you'd have some people unable to find mates, homosexual, asexual, choosing mates based off of genetic attraction, hang ups about miscegenation, occasional incest, excreta.

The 1000 number seems about right for an actual population. The Amish have known problems from their 200 member founder group. Quebec was founded by about 2600 without much trouble that I'm aware of.

[Tass]

Under ideal circumstances two would suffice. You could imagine a perfectly health but completely homozygoteous female and a male that is a copy of her except for a y-chromosome. Their offspring would basically be clones of them.

Inbreeding and lack of genetic variance only becomes a problem when the population needs to adapt, or when there are so many recessive disseases carried that the frequency of healthy offspring becomes to low to propagate the population.

[idobox]

There would still be mutations, and in a few generations you would end up with a population carrying possibly dangerous defects. Given the small starting number, a large fraction of them could carry it.
Also, they're going to bring a bunch of microorganisms with them that are going to continue to evolve. Genetic diversity is absolutely necessary for large organisms to adapt to the evolution of smaller ones, that's why nearly everything that's big enough to be seen by the naked eye has some form of sex.

The best solution, I insist, would be an all female crew and a few gallons of frozen sperm. In the beginning, you would use artificial insemination to keep genetic diversity high. The all female crew would be there to ensure high fertility, and get the fastest possible population growth. Once the population gets large enough, as each potential mother is less critical, you can reintroduce males, while still using frozen sperm to increase the genetic pool.
Normal breeding should be allowed only when the population is significantly larger than the minimum requirements for survival. 1% children with genetic defects might not endanger the group, but if waiting for another generation allows this number to drop to .1%, it would be criminal not to do it.