Decoding Life's History: Building Phylogenetic Trees

Biology Grades High School 10:56 Video
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Lesson Description

Learn how to construct and interpret phylogenetic trees (cladograms) to understand evolutionary relationships among species, using observable traits and genetic evidence.

Video Resource

Understanding and building phylogenetic trees | High school biology | Khan Academy

Khan Academy

Duration: 10:56
Watch on YouTube

Key Concepts

  • Phylogenetic Tree (Cladogram)
  • Common Ancestry
  • Derived Traits
  • Outgroup
  • Parsimony

Learning Objectives

  • Students will be able to define a phylogenetic tree and explain its purpose in representing evolutionary relationships.
  • Students will be able to identify and differentiate between ancestral and derived traits.
  • Students will be able to construct a simple phylogenetic tree based on provided trait data.
  • Students will be able to apply the principle of parsimony in constructing phylogenetic trees.

Educator Instructions

  • Introduction (5 mins)
    Begin by asking students what they know about evolution and how scientists determine relationships between different species. Briefly introduce the concept of a phylogenetic tree as a visual representation of these relationships.
  • Video Viewing (15 mins)
    Play the Khan Academy video "Understanding and building phylogenetic trees | High school biology | Khan Academy." Instruct students to take notes on key terms and concepts presented in the video.
  • Discussion and Clarification (10 mins)
    After the video, facilitate a class discussion to clarify any confusing points and reinforce key concepts like common ancestry, derived traits, outgroups, and parsimony.
  • Phylogenetic Tree Construction Activity (20 mins)
    Divide students into small groups and provide them with a set of hypothetical species and their corresponding traits. Have each group construct a phylogenetic tree representing the evolutionary relationships between the species, emphasizing the use of parsimony.
  • Presentation and Comparison (10 mins)
    Have each group present their phylogenetic tree to the class and explain their reasoning for the chosen arrangement. Compare and contrast the different trees, discussing the strengths and weaknesses of each.

Interactive Exercises

  • Trait Matrix Challenge
    Provide students with a trait matrix containing various organisms and their characteristics. Challenge them to construct a phylogenetic tree that best represents the evolutionary relationships among the organisms based on the principle of parsimony. This can be done individually or in small groups.

Discussion Questions

  • How does a phylogenetic tree represent evolutionary history?
  • What is the significance of the root and nodes in a phylogenetic tree?
  • Explain the principle of parsimony and why it is used in constructing phylogenetic trees.
  • How can genetic data be used to support or refute phylogenetic trees based on observable traits?

Skills Developed

  • Critical Thinking
  • Data Analysis
  • Problem Solving
  • Scientific Reasoning
  • Model Building

Multiple Choice Questions

Question 1:

What is the primary purpose of a phylogenetic tree?

Correct Answer: To represent the hypothesized evolutionary relationships among species

Question 2:

What does a node on a phylogenetic tree represent?

Correct Answer: A common ancestor

Question 3:

A trait that is shared by two or more taxa and originated in their most recent common ancestor is called a:

Correct Answer: Derived trait

Question 4:

Which of the following best describes an 'outgroup' in a phylogenetic tree?

Correct Answer: The group of organisms that is least related to the other species being studied.

Question 5:

What is the principle of parsimony in the context of constructing phylogenetic trees?

Correct Answer: Choosing the simplest explanation for evolutionary relationships

Question 6:

Which type of data is NOT used to construct phylogenetic trees?

Correct Answer: Astrological data

Question 7:

Rotating branches around nodes in a phylogenetic tree:

Correct Answer: Does not change the relationships depicted in the tree.

Question 8:

Why are phylogenetic trees considered hypotheses?

Correct Answer: They are based on limited data and are subject to change with new evidence.

Question 9:

In the video, which animal was used as the outgroup?

Correct Answer: Lamprey

Question 10:

What is the correct way to determine the evolutionary relationship between species?

Correct Answer: By comparing their genetic evidence and observable traits.

Fill in the Blank Questions

Question 1:

A _________________ tree is a diagram that depicts the evolutionary relationships among different species.

Correct Answer: phylogenetic

Question 2:

The most recent common ancestor of two species is represented by a _________ on a phylogenetic tree.

Correct Answer: node

Question 3:

A _________ trait is a characteristic that evolved in the ancestor of a group and is present in all its descendants.

Correct Answer: derived

Question 4:

The principle of _________ suggests that the simplest explanation is the most likely to be correct.

Correct Answer: parsimony

Question 5:

An _________ is a group of organisms that is less related than the other species being studied.

Correct Answer: outgroup

Question 6:

Molecular evidence such as differences in _________ and _________ can be used to construct a phylogenetic tree.

Correct Answer: protein, DNA

Question 7:

Phylogenetic trees are considered _________, meaning they are subject to revision with new evidence.

Correct Answer: hypotheses

Question 8:

The presence of _________ was one of the traits used to classify the animals in the video.

Correct Answer: jaws

Question 9:

Observable _________ are often used to construct phylogenetic trees.

Correct Answer: traits

Question 10:

The goal of constructing a phylogenetic tree is to understand how different species evolved from _________.

Correct Answer: ancestors

Educational Standards

B.LS4.1:Communicate scientific information that common ancestry and biological evolution are supported by multiple lines of empirical evidence. B.LS4.2:Construct an explanation based on evidence that biological diversity is influenced by (1) the potential for a species to increase in number, (2) the heritable genetic variation of individuals in a species due to mutation and sexual reproduction, (3) competition for limited resources, and (4) the proliferation of those organisms that are better able to survive and reproduce in the environment. B.LS4.4:Construct an explanation based on evidence for how natural selection leads to adaptation of populations.

Teaching Materials

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