Phylogenetic Tree Concepts

The video tutorial on molecular phylogenetics covers various aspects of tree topology and types of phylogenetic trees. It explains the differences between cladograms and phylograms, highlighting how they represent evolutionary relationships. The tutorial delves into tree topology, discussing dichotomy and polytomy, and explores the degree of tree resolution, including star, partially resolved, and fully resolved trees. It also distinguishes between rooted and unrooted phylogenetic trees and provides methods for converting unrooted trees to rooted ones using outgroup and midpoint approaches. The challenges in finding true tree topology due to computational complexity are also addressed. The video concludes with a preview of upcoming topics in phylogenetic analysis.

What is the main difference between a cladogram and a phylogram?

• Phylograms are unscaled, cladograms are scaled.

• Phylograms show genetic distance, cladograms do not.

• Cladograms show evolutionary time, phylograms do not.

• Cladograms have varying branch lengths, phylograms do not.

In a dichotomy, how many descendants does each ancestor give rise to?

• Four

• Three

• Two

• One

What is a star tree?

• A completely unresolved cladogram

• A fully resolved tree

• A tree with only polytomies

• A tree with only dichotomies

Which type of phylogenetic tree does not assume a common ancestor?

• Unrooted tree

• Rooted tree

• Cladogram

• Phylogram

What is the main advantage of a rooted tree over an unrooted tree?

• It is less informative.

• It provides direction of evolutionary paths.

• It shows relative relationships only.

• It does not require a common ancestor.

What is the purpose of using an outgroup in phylogenetic analysis?

• To determine the midpoint of a tree

• To identify the most recent common ancestor

• To root the tree by providing a reference point

• To calculate genetic distance

What assumption does the midpoint rooting approach rely on?

• All branches evolve at different rates.

• Outgroups are not needed.

• Divergence from root to tips is equal.

• The tree is fully resolved.

Why is finding a true tree topology considered difficult?

• It does not require any calculations.

• It requires a large number of taxa.

• The number of potential topologies is small.

• It is computationally demanding.

What does the formula for calculating the number of rooted trees depend on?

• The number of taxa

• The length of branches

• The presence of an outgroup

• The type of tree

What is the molecular clock hypothesis?

• It is used to determine the midpoint of a tree.

• Branch lengths are not proportional to evolutionary time.

• Mutations accumulate at constant rates over time.

• Molecular sequences evolve at varying rates.