Third, some populations lose genetic diversity and become fixed.
Seven of the 12 N10 populations became fixed over 20 generations. Six
of the seven populations became fixed for the wild-type allele (all/)
and one for the black allele (all b/b). On average, we expect equal
numbers of each type to be fixed if the alleles are not subject to selection,
given that the two alleles were equally frequent initially. None of
the large populations became fixed over the 20 generations.