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Unformatted text preview: ). We summarized the essentiality relationship between parental gene–new gene
pairs and found that the parental gene of a young
essential gene can be either essential or nonessential, and vice versa (tables S10 and S11). These data
suggested that a new essential gene can rise from
either an essential or a nonessential parent (given
that it represents the ancestral state of essentiality)
and that either essential genes or nonessential genes
can give rise to each type of gene. These processes
appeared to be relatively independent (table S11,
Fisher’s Exact test, two-tailed, P = 0.296).
A previous case study of the sterile phenotype
of a paternal-effect gene suggested that genes
essential for fertility could arise in 10 My (26).
Our observation of lethal phenotypes caused by
the knockdown of young genes suggested that
essential vital genes have been frequently generated in recent evolutionary periods. A new gene
might not have become essential immediately
after its origination. It, however, can integrate
into a vital pathway by interacting with existing
genes, and such interaction would be optimized
Wolpert et al., 2e, Fig.This coevolution may
by mutation and selection. 12.14
lead to the new gene becoming indispensable. This
observation is supported by our modeling (8) with
large-scale interaction data (27, 28), revealing
genome-wide interactions of young essential genes
with many previously unrelated genes (fig. S6).
The mechanism for the evolution of essentiality would change with the types of new genes. A
de novo gene has to evolve essentiality through
neofunctionalization because it has no ancestral
template. A duplicated gene, generated from an
ancestral copy of its parental gene, could become Nance et al (2003).
Development 130:5339-5350 Supporting Online Material
Materials and Methods
Figs. S1 to S8
Tables S1 to S11
References PIE-1 par genes are required for partitioning of
germ plasm into the germ cell lineage 11 August 2010; accepted 1 November 2010
10.1126/science.1196380 cursors (P blastomeres) during the first embryonic divisions (Fig. 1A) (2). Like embryonic germ
granules of other organisms, P granules have been
hypothesized to harbor the determinants that specify the germlin...
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