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Learning Exercise

Material: Homology and Evolution
Submitted by: Nancy J. Pelaez on May 31, 2003
Date Last Modified: May 31, 2003
Title: Homology Provides Evidence for Evolution
Description: This assignment was completed by a pair of college students in a science teacher education class. The assignment is for use in a high school biology class.
Time Required Five (53 min.) class sessions to work on your project. Two periods for research. Two periods for creating a powerpoint report an
Topics: Homology, Evolution, Convergent evolution, cladistics
Course: BIOL409 Teaching Evolution: Online Course for Teachers (Assigntment for use at the HS level)
Prerequisites Skills: PowerPoint and web navigation skills.
Learning Objectives: Students explore the idea of homologies and how they fit into the theory of evolution. A homology is a structural similarity among organisms. Often these structural similarities have been employed for vastly different functions in various species. The task is to research scientific journals, books, and computer Internet cites to find information on homologous structures. Take the information and use it to create a power point presentation showing how homologous structures provide evidence for evolution. Self-assess using the grading rubric provided to insure that the presentation you create is formatted correctly and includes all the requisite content. The presentation should include at least three examples showing a comparison of homologous structures between species.
Text of Learning Exercise: Dolphin, Wolf, Shark

1. Compare the picture of the limbs of the dolphin, shark, and wolf. Are the
bones inside the dolphin's flipper more similar to the wolf's leg are the sharks
fin? Justify your answer.

2. Compare the jaws of the wolf to those of the dolphin and the shark. Is the
structure of the wolf's jaw closer to the dolphin or the shark? Justify your

3. Look at the pictures of the three skulls (craniums). Which two skulls seem
the most similar. Justify your answer.

4. Draw the "correct" evolutionary tree showing the relationship between a wolf,
a dolphin, and a shark.

5. What living group do sharks, dolphins, and wolfs have in common (out-group)?
Add the out-group to the evolutionary tree you drew for question #4.

Bear, Opossum, Raccoon

6. Raccoons and opossums look alike but they actually belong to two different
groups of mammals: the placentals and the marsupials. Do bears belong to the
placenta or "pouch" group? Justify your answer.

7. Compare the newborn bear, opossum and raccoon for signs of physical maturity.
Which pair seems most closely related? Justify your answer.

8. Compare the DNA sequence of the bear, raccoon, and opossum. The pair that
shares the most sequences are the closest living relatives. Is the raccoon a
closer relative of the bear or the opossum? Use the DNA evidence to justify your

9. Draw the "correct" evolutionary tree showing the relationship between a bear,
opossum, and a raccoon. Include the echidna as the "out group".

10. What is one difference between the echidna and the other three animals?

Human, Tunicate, Sponge

11. Humans obviously have brains; does a tunicate have a brain? Does a sponge
have a brain?

12. What is a notochord? Which two species have notochords during their

13. Look at the picture of the developing human. What are two characteristics
that a developing human embryo has but that later disappear?

14. Compare the DNA sequence of the tunicate, sponge, and human. The pair that
shares the most sequences are the closest living relatives. Is the human a
closer relative of the tunicate or the sponge? Use the DNA evidence to justify
your answer.
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