  Whole genome duplication (WGD) is one of the most important events in the
molecular evolution of organisms. In fish species, a WGD is considered to have
occurred in the ancestral lineage of teleosts. Recent comprehensive ortholog
comparisons among teleost genomes have provided useful data and insights into
the fate of redundant genes generated by WGD. Based on these data, a
mathematical model is proposed to explain the evolutionary scenario of genes
after WGD. The model is parameterized taking into account an equilibrium
between i) rapid loss of either of the duplicate genes and ii) moderate
functional differentiation of each of duplicate genes, both of which are
followed by slow gene loss under purifying selection. This model predicts that,
in the teleost lineage, a maximum of about 3000 gene pairs may have
differentiated functionally during 90 million years after WGD. Thus, the
present study provides a possibility that the whole impact of WGD can be
quantitatively assessed according to the model parameters, before details of
genomic structural changes or functional differentiation are investigated. If
the equilibrium model is valid not only for teleosts but also for other
lineages that have undergone WGDs, correlations between the assessment indices
and evolutionarily significant events, such as the diversification of species
or the occurrence of novel phenotypes, could be tested and compared among those
lineages.
