Difference Between Rooted and Unrooted Phylogenetic Tree

Key difference – Rooted vs Unrooted Phylogenetic Tree
 

Phylogeny is an important field that explores the life on earth through the time. It reveals the connection between organisms with their ancestors and descendants. The relationships between organisms are diagrammatically represented by various tree-like representations such as dendogram, cladogram, phenogram, phylogram, etc. A phylogenetic tree is a branching tree-like diagram which explains the phylogenetic relationships between organisms with the amount of evolutionary distance. There are two main types of phylogenetic trees known as rooted and unrooted. The key difference between the rooted and unrooted phylogenetic tree is that rooted tree shows the most basal ancestor of the tree while unrooted phylogenetic tree does not show an ancestral root.

CONTENTS
1. Overview and Key Difference
2. What is a Rooted Phylogenetic Tree
3. What is an Unrooted Phylogenetic Tree
4. Side by Side Comparison – Rooted vs Unrooted Phylogenetic Tree
5. Summary

What is a Rooted Phylogenetic Tree?

A rooted phylogenetic tree serves as a useful diagram which shows the evolutionary history. It has a basal node which is called the root, representing the common ancestor of all the groups of the tree. The root of a tree is considered as the oldest point in the tree which represents the last common ancestor of all groups included in the tree. Hence, a rooted tree shows the direction of evolutionary time. From a single species of a rooted tree, the common ancestry or the species ancestor can be found by tracing back to the basal node. Since the rooted tree depicts the direction of evolutionary time, it is easy to find the older or newer groups it has. A rooted tree can be used to study the entire groups of organisms. Accurate rooting of a phylogenetic tree is an important and crucial factor since inaccurate rooting can result in wrong interpretations of genetic changes between organisms and their directionality of the evolution.

What is an Unrooted Phylogenetic Tree?

An unrooted phylogenetic tree is a phylogenetic diagram which lacks a common ancestor or a basal node. This type of a tree does not indicate the origin of evolution of the groups of interest. It depicts only the relationship between organisms irrespective of the direction of the evolutionary time line. Therefore, it is difficult to study the evolutionary relationships of the groups with respect to time using an unrooted tree.

There are two main ways to root an unrooted phylogenetic tree. They are

• Finding an outgroup – This requires prior knowledge about the relationships between taxa. Then a taxon which lies outside the group can be used as an outgroup to draw a rooted phylogenetic tree

• Finding the midpoint or distance – The midpoint of the most distant two taxa in the tree can be assumed as a root for the phylogenetic tree.

What is the difference between Rooted and Unrooted Phylogenetic Tree?

Summary –  Rooted vs Unrooted Phylogenetic Tree

A phylogenetic tree represents the evolutionary pathways and connections between organisms using a branched tree-like diagrams. Phylogenetic tress can be rooted or unrooted. A rooted tree has a node at the base, representing the common ancestor which connects all interest groups. An unrooted tree shows the relationships between organisms. However, it does not depict the common ancestor that all the groups share. This is the difference between rooted and unrooted phylogenetic tree.

References:
1. “Tree” Facts: Rooted versus Unrooted Trees.” National Center for Biotechnology Information. U.S. National Library of Medicine, n.d. Web. 04 Apr. 2017
2. Graham, Sean W., Richard G. Olmstead, and Spencer C. H. Barrett. “Rooting Phylogenetic Trees with Distant Outgroups: A Case Study from the Commelinoid Monocots.” Molecular Biology and Evolution. Oxford University Press, 01 Oct. 2002. Web. 04 Apr. 2017