Phylogenetic tree
A phylogenetic tree is a tree showing the evolutionary interrelationships between various species or other entities that are believed to have a common ancestor. A phylogenetic tree is a form of cladogram.In a phylogenetic tree, each node with descendants represents the most recent common ancestor of the descendants, and edge lengths correspond to time estimates.
A rooted phylogenetic tree is a directed tree with a unique node corresponding to the (usually imputed) most recent common ancestor of all the entities at the leaves of the tree.
Here is an example
of a rooted phylogenetic tree, which has been colored according to the three
domain system [Woese
1998]:
An unrooted phylogenetic tree is, loosely speaking, a tree derived from a rooted phylogenetic tree by omitting the root. More precisely, it is a forest of rooted phylogenetic trees depicted so that the roots are all linked. Here is a thumbnail of an unrooted tree¹:
This shows a phylogenetic tree for myosin, a superfamily of proteins. The full image of this tree can be viewed by following this link: Myosin Phylogenetic Tree
Links to other pictures are given in the Pictures on the web subsection below.
Caveats
- By
their very nature, phylogenetic trees hide any hybridization
and lateral gene transfer [Woese
2002] that may have taken place. For these reasons, the proposed PhyloCode (see
External Link below) does not assume a tree structure.
- The phylogenetic
tree of a single gene or protein taken from a group of species often differs from
similar trees for the same group of species, and therefore great care is needed
in inferring phylogenetic relationships amongst species.
- Trees that do not include extinct species must also be interpreted with care.
See also
Footnote
- T.
Hodge, M.J.T.V. Cope (2000) A Myosin Family Tree. Journal of Cell Science
113, 3353-3354. See also the Myosin external link below.
References
- C.R. Woese, "The Universal Ancestor", Proceedings of the National Academy of Sciences, 95:6854-6859 (1998).
- C.R. Woese, "On the evolution of cells", Proceedings of the National
Academy of Sciences, 99:8742-7 (June 25, 2002).