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.
- 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.
- 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.
Pictures on the web