Systematics Based on Evolutionary
Relationships: Cladistics and Phylogeny
by CHED on June 17, 2017
lesson duration of 0 minutes
under General Biology 2
generated on June 17, 2017 at 11:44 pm
Tags: Systematics Based on Evolutionary Relationships: Cladistics and Phylogeny
CHED.GOV.PH
K-12 Teacher's Resource Community
Generated: Jun 18,2017 07:44 AM
Systematics Based on Evolutionary Relationships: Cladistics and Phylogeny
(
3 hours )
Written By: CHED on July 18, 2016
Subjects: General Biology 2
Tags: Systematics Based on Evolutionary Relationships: Cladistics and Phylogeny
Resources
n/a
n/a
Content Standard
Basic Taxonomic Concepts and Principles, Description, Nomenclature, Identification, and Classification
Performance Standard
n/a
Learning Competencies
Describe species diversity and cladistics, including the types of evidence and procedures that can be used to establish
evolutionary relationships.
Introduction 30 mins
Communicating Learning Objectives
1. Introduce the following learning objectives using any of the suggested protocols (Verbatim, Own words, Readaloud)
I. I can demonstrate how shared derived characters can be used to reveal degrees of relationship.
II. I can build cladograms to infer evolutionary relatedness.
Teacher Tip: Here are some definition of terms:
PhylogenyPhylogeny- the evolutionary relationships among organisms
CladogramCladogram- a phylogenetic tree that shows relationship of taxa based on shared derived characters
1/6
CHED.GOV.PH
K-12 Teacher's Resource Community
Character- any trait of an organism that can be described or measured
Character statestate- describes the character. A particular character can have several character states
Example: Corolla is a character. Character states can be: shape of the corolla, color of corolla, number of petals
comprising the corolla.
Homologous characters - characters having similar structures because these were derived from a common ancestor
Analogous characters-characters
characters-characters that have separate evolutionary origins, but are superficially similar because they
perform the same function. Analogous characters are the result of convergent evolution.
Example: Bird and bat wings are analogous since both are used for flying.
Clade- a group of taxa consisting of an ancestor and all of its descendant taxa
Review
1. Say, “Look around you, and see the enormous diversity the natural world has to offer. However, amidst such
diversity is also an amount of similarity which you can observe. This gives us the idea that somehow, organisms are
indeed related. Life is somehow interconnected to each other.” Systematics is the study of the diversity of organisms
in the evolutionary context. It intends to use phylogeny in classifying organisms. Phylogeny is the study of the
evolutionary history and relationships among organisms. Evidences from a wide variety of sources including
paleontology, embryology, morphology, anatomy and molecular biology can be used to establish phylogeny. Over the
last few centuries systematists have developed different approaches to show relationships among organisms. The
most commonly used is cladistics.
2. Discuss briefly:
Cladistics studies relationships between taxa using shared derived characters. The basic assumption behind
cladistics is that members of a group share a common recent ancestor and are thus more "closely related" to one
another than they are to other groups of organisms. Related groups of organisms are recognized because they share
a set of derived characters. These derived characters were inherited from a recent ancestor.
3. Ask your learner to define the following terms in their own words:
I. analogous character
II. character
III. character state
IV. clade
V. cladogram
VI. homologous character
VII. phylogeny
4. Stress that similarities among existing organisms (including morphological, developmental, and molecular
similarities) reflect common ancestry and provide evidence for evolution.
I. Outline:
2/6
CHED.GOV.PH
K-12 Teacher's Resource Community
A. shared derived characters can be used to reveal degrees of relationship
B. constructing and interpreting a phylogenetic tree
Motivation 20 mins
Café Conversation
1. Ask learners: “Do you remember the last time you had a family reunion? A summer vacation or a family barbecue
and the latest family picture taken together? Can you describe your family members? What makes you similar to them
and what makes you unique?”
2. Ask learners to list characters or features that served as evidences (e.g. morphological, genetic, etc.) that indeed
they belong to the same family. Ask learners to note as many as they can think of.
Teacher Tip: Suggestion: Include a website or video that learners can view to understand how to construct a
cladogram. Explain the rationale of the activity.
Sample responses:
• Color of the eyes (e.g. brown, black)
• Texture and color of the hair (e.g. curly black hair)
• Color of the skin (e.g. fair complexion)
• Blood type (e.g. A, AB, O, B)
• Height
• Shape of the nose
3. Explain, “Basically, a family picture represents a family tree. Family trees show how people arerelated to each
other. Similarly, scientists use phylogenetic trees like cladograms to study the relationships among organisms.
Sometimes, family trees are used to show relationships between individuals. Those who are closely related are located
closer together than those who are onlydistantly related. For instance, in a family tree, we can see that the siblings are
close together, indicating a close genetic relationship. But the siblings are far from their great aunt, indicating a more
distant genetic relationship. Family trees can also be used to see ancestral connections. Thatis, we can see that all the
people in the last generation have the same great-great-grandparents in common.
This same idea of relationships can be used in science. Biologists use phylogenetic trees to illustrate evolutionary
relationships among organisms.
4. Stress that for the succeeding activities, focus will be on constructing and interpreting a simple phylogenetic tree.
Teacher Tip: Constructing a phylogenetic tree is one way to visualize evolutionary relatedness. In this activity,
guide learners on how to construct their own tree from a set of animals provided, using only observable
physical features. This activity gives learners an opportunity to classify organisms on their own, and they can
visualize the types of evidence used to show evolutionary relationships.
Due to the open-ended nature of this activity, learners will come up with many different combinations and
layouts. However, the end result should be an evolutionary tree that shows the basic relationship among
animals. Arthropods such as the spider and moth should be far apart from an aquatic mammal such as the
walrus.
3/6
CHED.GOV.PH
K-12 Teacher's Resource Community
This is also a good opportunity to gauge how well learners understand the basis of different classifications,
such as reptile, amphibian, and mammal.
Phylogenetic systematics emphasize descent and common ancestry in order to determine the evolutionary
history of groups of organisms as a determining factor in classification
Instruction 50 mins
Discussion:
A. shared derived characters can be used to reveal degrees of relationship
B. constructing and interpreting a phylogenetic tree
Work in Pairs and Build that Tree
1. Ask learners to choose a partner and work in pairs.
2. For this activity, present to learners a diverse group of vertebrates and ask them to make a phylogenetic tree
showing their evolutionary relationships. This tree should be primarily based onphysical
onphysical characteristics,
characteristics, such as:
I. Presence or absence of a backbone
II. Ability to breathe in air or water
III. Cold or warm blooded
IV. Carnivore, herbivore, or omnivore
V. Presence or absence of hair/fur
VI. Any other external structures such as horns
Note: The following outline drawings of animals are provided for the activity. These can be printed and cut out for
learners to work with.
3. Ask learners to work in pairs and individually cut out each animal, including the name.
4. Ask them to lay all the animals on their desks and separate them into two groups using the presence or absence
of a backbone as the first character.
5. On a separate sheet of paper, start constructing the phylogenetic tree like the one shown below.
4/6
CHED.GOV.PH
K-12 Teacher's Resource Community
6. Ask learners to continue separating the animals into smaller groups using the characters in number two.
7. When an animal reaches the tip of the branch, glue it. Repeat for all other animals in the
collection.
8. Ask volunteers to present their phylogenetic tree in class.
Practice 40 mins
1. Learners will still work in pairs.
2. Ask each pair to construct a cladogram based on the data provided.
Constructing a Cladogram
1. Ask learners to use the data below to arrange the groups of organisms based on their shared derived traits. This
time you will be using distantly related organisms or a taxon termed an outgroup.
2. For each group, the traits or characters are already listed. For each character, determine which state is ancestral or
primitive and which is derived. This is usually done by comparing with the outgroup. Traits found in the outgroup are
likely to be ancestral or primitive. Similarly, traits not found in the outgroup are considered as derived. In cladistics, it is
the derived trait shared among taxa that should be placed in the cladogram.
3. Group taxa according to their shared derived character(s).
4. Once you have evaluated all the characters, you may start constructing your cladogram. Where do you place the
outgroup?... (Correct, an outgroup is always placed at the base of the cladogram.)
5. Choose a learner to present the cladogram. After this, show them the correct cladogram below.
Enrichment 30 mins
5/6
CHED.GOV.PH
K-12 Teacher's Resource Community
1. Now you're getting the hang of this! Once again, use the data below to arrange organisms based on their shared
derived characters. This time work again with your partner and test your skill in building a cladogram.
cladogram.
Of course, this was just an example of the tree-building process. Phylogenetic trees are generally based on many
more characters and often involve more lineages. For example, biologists reconstructing relationships between 499
lineages of seed plants began with more than 1,400 molecular characters.
Evaluation 10 mins
1. Go online. Choose a group of organisms you are interested to work with (e.g. invertebrates);
2. Download pictures of different species.
3. Print the pictures. In tabular form, list all the characters. Evaluate the characters (whether primitive or derived).
4. Remember that in building your cladogram, use only shared derived characters.
5. Construct your own cladogram.
6. Share this with your seat mate and discuss your cladogram.
7. The outputs may be submitted as soon as it is discussed.
8. Learners can compare their work and provide each other with feedback (peer assessment). Remind learners to
make specific suggestions and recommendations and what could be improved. Ask for difficulties they encountered
and strategies used to make the task easy.
Generated: Jun 18,2017 07:44 AM
6/6
Powered
Poweredby
byTCPDF
TCPDF(www.tcpdf.org)
(www.tcpdf.org)