Navigation Links
Phylogenetic tree


Fig. 1: A rooted tree for rRNA genes
Fig. 2: Unrooted tree for myosin gene

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 tree¹ for myosin, a superfamily of proteins. Links to other pictures are given in the Pictures on the Web subsection below.

There are three main methods of constructing phylogenetic trees: Distance based methods such as Neighbour Joining, Parsimony based methods such as Maximum Parsimony , and character based methods such as Maximum Likelihood or Bayesian inference.

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

  1. 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

External links

Pictures on the web

General


'"/>


(Date:9/18/2014)... characters, so you might expect that most would have ... some dogs are distinctly more pessimistic than others, research ... research is exciting because it measures positive and negative ... researchers and dog owners an insight into the outlook ... Starling, from the Faculty of Veterinary Science. Her PhD ...
(Date:9/18/2014)... people are too stressed they are often grouchy, grumpy, ... Institute (BMI) at EPFL have just highlighted a fundamental ... and the loss of social skills and cognitive impairment. ... regulatory molecule in the brain. This was revealed by ... , Carmen Sandi,s team went to look for answers ...
(Date:9/17/2014)... reproductive technologies, the justice and well-being of our ... identify key issues, articulate their values and concerns, ... defensible ways forward. But what are the best ... Hastings Center and the Presidential Commission for the ... publish a series of essays to highlight the ...
Breaking Biology News(10 mins):Dogs can be pessimists too 2Dogs can be pessimists too 3How stress tears us apart 2Why bioethics literacy matters 2Why bioethics literacy matters 3
... the forehead becomes higher, the hair at the back of ... suffers from greater or lesser hair loss. There are hardly ... and tinctures. , It has long been suspected that hereditary ... now it was unclear which genes are involved. The researchers ...
... in the Journal of Biological Chemistry, scientists report that ... and inert role in cells is actually involved in ... the researchers were able to sensitize drug resistant breast ... appears as the "Paper of the Week" in the ...
... virus that infects bacteria by injecting its genomic DNA ... driving force behind this poorly understood injection process, which ... the release of pressure accumulated within the viral particle ... are formed of a capsid structure, or head, in ...
Cached Biology News:Tendency to hair loss inherited from the mother 2New polysaccharide may help combat multidrug resistance in cancer 2Basis for DNA ejection from single phage particles 2
Other biology definitionOther Tags