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Fig. 3.
Schematic predictions of two models of developmental constraints on
evolution.
duplication (e.g. duplicate genes could acquire lower expression in early
development) as well as of biased retention and loss. To check this, we
used expressed sequence tag (EST) data to determine expression in
mouse development: the orthologs of genes kept in duplicate in fish are
lowly expressed in early mouse development. Moreover, the data fit a
simple linear correlation, while excluding the parabola curve expected
from the hourglass model (Fig. 3). The same results are obtained when
we investigate biased gene retention after whole-genome duplications
at the origin of vertebrates. Finally, gene KO phenotypes are also con-
sistent with decreasing constraints over development in both zebrafish
and mouse.
Taken together, these results show that (a) timing of expression dur-
ing development is a strong and conserved constraint on genome evolu-
tion; (b) gene duplication is restricted when phenotype is constrained;
and (c) at the genomic level, the traditional von Baer-like model provides
a better fit than the hourglass model.
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