Biology Reference
In-Depth Information
superfamily.
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By combining this gene tree with the known species phy-
logeny, we can date not only duplications, but losses as well. On a rooted
tree, events that are closer to the tips are more recent, and events closer
to the root are more ancient. This does not provide an absolute dating
(in years), but it does provide a relative dating. If we start with human
RARs (Fig. 1), we see that all speciations among vertebrates
Fig. 1.
Simplified phylogenetic tree of three groups of nuclear receptors: maximum
likelihood phylogeny (PhyML,
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JTT model, four rate categories, gamma shape
parameter, and proportion of invariant estimated) of 78 nuclear receptors from the
groups NR1B (RAR), NR1D (Rev-erb, E75), and NR1F (ROR, HR3). Branch
length is proportional to substitutions per amino acid site. The relative timing of key
speciation events is shown in blue, and the relative timing of duplication events is
shown in red.
