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in yeast. An important aspect of the work of Davis and Petrov
59
was to
use estimates of selective pressure that are phylogenetically independent
of the duplication. We conducted a similar study in fish,
57
and found that
these conclusions also applied to a more ancient genome duplication in a
vertebrate lineage. The selective pressure was measured by the number of
the number of nonsynonymous substitutions per site (d
N
) to the number
of synonymous substitutions per site (d
S
) between the human and mouse
orthologs of genes that either lost one copy (singletons) or were kept as
duplicates after the fish whole-genome duplication (Fig. 2). Using only
human-mouse d
N
to measure the rate of evolution of the encoded pro-
teins, we found that nonduplicated orthologs of gene pairs retained after
duplication evolve 30% slower. This is comparable to observations for
nematode (25%) and yeast (50%) genes.
What is the relevance of these observations to evo-devo? First, if
whole-genome duplication has really played a key role in the establish-
ment of the developmental diversity of fish
60,61
(but see Donoghue and
singletons
whole-genome duplication duplicates
paralog 1
paralog 2
d
N
= 0.056
d
S
= 0.48
d
N
/d
S
= 0.11
d
N
= 0.043
d
S
= 0.45
d
N
/d
S
= 0.097
duplication
more selection
p
< 10
-4
Fig. 2.
Comparison of selection pressure on duplicated and singleton genes.
Schematic phylogenetic classification of genes according to duplication and loss.
d
N
is the number of nonsynonymous substitutions per site, and d
S
is the number of
synonymous substitutions per site. The arrow represents the unpaired
t
-test between
d
N
/d
S
values.
