Assume a colony space ship to Alpha Centauri is under construction. The ship's mission is to land on an Earth-like planet in that system and to build a permanent human colony. Mass is at a premium, meaning there's pressure to put the minimum number of crew on the ship to establish a genetically healthy human population on the planet that could endure indefinitely and grow arbitrarily large without risk of inbreeding.
What is the minimum number of humans that could do this?
This article suggests the space ship's crew could be as small as 80 people, but I think it could be even smaller. https://www.newscien...ed#.VBiC_XtDLwo
Consider the fact that having a child with your first cousin--a person who shares 1/8 (12.5%) of your DNA--only doubles the risk of the child having genetic problems:
The risk of having a baby with birth defects – usually heart or nervous system problems which can sometimes be fatal – is still small, but it rises from 3% in the general Pakistani population to 6% among those married to blood relatives. The researchers also found a doubling of the risk in the babies of white British women who were over the age of 34. That increased risk, rising from 2% to 4%, is already known.
The slight increase in risk owes to the fact that relatives are likelier to share recessive genes for disorders. However, if the initial group of astronauts were screened for genetic disorders and selected on the basis of having the fewest mutated genes, then it would stand to reason that marriages between first cousins of their descendants would carry fewer risks. Moreover, if preimplantation genetic diagnosis were used for all pregnancies, then the risk of first cousins having inbred children might drop to 0%.
Based on this, I think the minimum size of a group of humans who want to found a genetically healthy human population could be as low as eight unrelated people (four women and four men), but their descendants would have to pay careful attention to genealogical records to avoid marrying "strangers" who were actually more related to them than believed. Just to minimize that problem for the sake of quality of life and personal freedom, I'd up the founder population size to 16 unrelated people. (If breeding with a first cousin who shares 12.5% of your DNA only raises the odds of having an inbred child slightly, then breeding with someone who shares 6.25% of your DNA might carry no extra risk.)
What do you guys think?