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To use the Fundamental Theorem we plot
as a function of
(Figure 1). The Fundamental Theorem now tells
us that allele frequencies have to change from one generation to the
next in such a way that
, which can only happen if
. So viability selection will cause the frequency of the
allele to increase.
Figure 1:
With directional selection (in this case
) viability selection leads to an ever increasing frequency of
the favored allele. Ultimately, the population will be monomorphic
for the homozygous genotype with the highest
fitness.
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Kent Holsinger
2008-08-25