A 'generation ship' could be just a bio-lab and genetic material (possibly digitized) that is grown into life only after the destination is reached. Or after it is terraformed by other genetically altered organisms, engineered on-site by AI (or by Earth-based scientists, at the cost of a few communication round-trips).
And this is just the most basic version someone from the 21st century would come up with.
Edit as reply because I am "posting too fast": From TFA: We are not gods
A cheap way of dismissing what is already, today, nearly working technology - artificial wombs [1], and building genomes from scratch [2]. Further, what I proposed is basically equivalent to seeds - as in literal, existing plant seeds. But we won't be able to replicate, in 10000 years of technological progress, what nature already has working? Such a claim requires showing some strong, fundamental barrier, not to have the possibility handwaved away with "we are not gods".
What technological progress can't be dismissed with "we are not gods"? Landing on the moon? Splitting the atom? Heart transplants? Heavier-than-air flight? Fire?
[1] https://en.wikipedia.org/wiki/Artificial_womb
[2] https://www.theguardian.com/science/2010/may/20/craig-venter...