Alternative calculation of equilibrium allele frequency (
) under heterozygote
advantage (Overdominance)Note that the top line is equivalent to (p)(
) = W0p2
+ W1(pq)which reduces to the final
sAAfA = saafa
which can be written in terms of s coefficients and q as
(s1)(1-q) = (s2)(q)
s1 - s1q = s2q
s1 = s2q + s1q
s1 = (s2 + s1)(q)
(s1)) / (s2 + s1) = q =
"Overdominance"
is an unfortunate term, as 'dominance' is a
relationship among alleles at a locus, but is applied
here to describe the fitness phenotype of the Aa
genotype. The companion term "underdominance"
to describe heterozygote disadvantage creates the
same problem. Like use of 'gene' when we mean 'allele',
the latter terms are too well established to discard outright,
but should be used sparingly.
Figure © 2013 by Sinauer; Text material © 2021 by Steven M. Carr