What is the Difference Between Rooted and Unrooted Phylogenetic Tree

The main difference between rooted and unrooted phylogenetic tree is that the rooted phylogenetic trees show the ancestry relationship, whereas the unrooted phylogenetic trees only show the relatedness of organisms. Furthermore, each descendant of the rooted phylogenetic tree has a most recent common ancestor, while unrooted phylogenetic tree does not show the ancestral root. 

In overall, rooted and unrooted phylogenetic tree are two types of phylogenetic trees that describe the relationships among organisms. 

Key Areas Covered 

1. What is a Rooted Phylogenetic Tree
     – Definition, Features, Importance
2. What is an Unrooted Phylogenetic Tree
     – Definition, Features, Importance
3. What are the Similarities Between Rooted and Unrooted Phylogenetic Tree
     – Outline of Common Features
4. What is the Difference Between Rooted and Unrooted Phylogenetic Tree
     – Comparison of Key Differences

Key Terms 

Ancestry, Recent Common Ancestor, Relatedness, Rooted Phylogenetic Tree, Unrooted Phylogenetic Tree

What is a Rooted Phylogenetic Tree 

A rooted phylogenetic tree is a type of phylogenetic tree that describes the ancestry of a group of organisms. Importantly, it is a directed tree, starting from a unique node known as the recent common ancestor. Basically, the roots of the phylogenetic tree describe this recent common ancestor. 

Figure 1: A Rooted Phylogenetic Tree

However, this recent common ancestor is an extra and distantly-related organism to the group of organisms used to build up the phylogenetic tree. But, it serves as the parent of all organisms in the group.  

What is an Unrooted Phylogenetic Tree 

The unrooted phylogenetic tree is a type of phylogenetic tree that only describes the relatedness of a group of organisms. Importantly, the leaf nodes of this type of phylogenetic tree only show relatedness, not the ancestry. Hence, it does not start with the recent common ancestor and does not contain a root. 

Figure 2: An Unrooted Phylogenetic Tree

However, the same data in the rooted phylogenetic tree can be used to generate an unrooted phylogenetic tree as well. It is created by omitting the root.  

Similarities Between Rooted and Unrooted Phylogenetic Tree 

• Rooted and unrooted phylogenetic trees are two types of phylogenetic trees, describing the relationships among organisms. 
• Moreover, both types of trees give an idea about the relatedness of organisms. 
• Additionally, both of them contain leaf nodes and internal nodes. 

Difference Between Rooted and Unrooted Phylogenetic Tree 

Definition 

Rooted phylogenetic tree refers to a phylogenetic tree that shows the ancestry relationship, while unrooted phylogenetic tree refers to the phylogenetic tree that only shows the relatedness of organisms. Thus, this is the main difference between rooted and unrooted phylogenetic tree.

Components 

Moreover, rooted phylogenetic trees contain a root, internal nodes, and leaf nodes, while unrooted phylogenetic trees contain leaf nodes and internal nodes only but not the root.  

Types of Organisms 

Furthermore, rooted phylogenetic trees contain related organisms as well as an extra, distantly-related organism for the root, while unrooted phylogenetic trees only contain related organisms. 

Common Ancestor 

Also, another important difference between rooted and unrooted phylogenetic tree is the common ancestor. A rooted phylogenetic tree shows the recent common ancestor, which is the root for each descendant, while the unrooted phylogenetic tree does not show any common ancestor. 

Evolutionary Path 

Besides, each root to a node in the rooted phylogenetic tree shows the evolutionary path, while unrooted phylogenetic tree does not specify the evolutionary path.  

Ancestral State of Organisms or Genes 

The rooted phylogenetic tree shows the ancestral state of organisms or genes at the bottom to the terminal branches, while the unrooted phylogenetic tree does not show the ancestral state. Thus, this is also a difference between rooted and unrooted phylogenetic tree.

Conclusion 

Basically, a rooted phylogenetic tree is a type of phylogenetic tree with a root, describing the recent common ancestor. Moreover, each root to a node on the tree shows the evolutionary path. On the other hand, the unrooted phylogenetic tree is another type of phylogenetic tree, only describing the relatedness of a group of organisms. Therefore, there is no recent common ancestor and evolutionary path. Hence, the main difference between rooted and unrooted phylogenetic tree is the presence of a recent common ancestor. 

References:

1. “Phylogenetic Trees.” Phylogenetic Trees, Available Here.

Image Courtesy:

1. “Phylogenetic tree” By This vector version: Eric Gaba (Sting – fr:Sting) – NASA Astrobiology Institute(Public Domain) via Commons Wikimedia   
2. “Unrooted c17orf98 Phylogenetic Tree” By Elfst022 – Own work (CC BY-SA 4.0) via Commons Wikimedia