Home > Phylogenetic tree
A phylogenetic tree is a tree showing the evolutionary interrelationships among various species or other entities that are believed to have a common ancestor. A phylogenetic tree is a form of a 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. Each node in a phylogenetic tree is called a taxonomic unit. Internal nodes are generally referred to as Hypothetical Taxonomic Units (HTUs) as they cannot be directly observed.
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. Figure 1 depicts 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. Figure 2 depicts an unrooted phylogenetic treeš for myosin, a superfamily of proteins. Links to other pictures are given in the Pictures on the Web subsection below.
1 Caveats
- The phylogenetic tree of a single geneDNA and to a chromosome (right). Introns are regions often found in eukaryote genes which are removed in the splicing process: only the exons encode the protein. This diagram labels a region of only 40 or so bases as a gene. In reality many genes are much 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.
2 See also
- dendrogram
- endosymbiosis
- phylogenyA phylogeny (or phylogenesis) is the origin and evolution of a set of organisms, usually of a species. A major task of systematics is to determine the ancestral relationships among known species (both living and extinct), and the most commonly used method
- evolutionary treeThe evolutionary tree of living things is currently supposed to run something along the lines of that listed below. Most of the tree was based on ideas from cladistics; where more than two groups are shown in a single branch, there is disagreement about h
- taxonomyTaxonomy may refer to either a hierarchical classification of things, or the principles underlying the classification. Almost anythinganimate objects, inanimate objects, places, and eventsmay be classified according to some taxonomic scheme. Mathematicall
- tree structureTrees (structure) A tree structure is a way of representing the hierarchical nature of a structure in a graphical form. It is named a "tree structure" because the graph looks a bit like a tree, even though the tree is generally shown upside down compared
3 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.
4 References
