7Th Grade Life Science: Activity Outline

Evolutionary Relationships 2009

Name: ______Period: ____ Purpose/Objectives: During this activity, you will use different lines of evidence (body structure and molecular structure) to infer the evolutionary relationship among several animals. You will then construct a phylogenetic tree that illustrates how these species relate to each other based on similarities in morphology and DNA sequence. By the end of this exercise, you should be able to:  State evidence that supports the theory of evolution.  Explain how scientists infer evolutionary relationships among species.  Explain how a branching (phylogenetic) tree diagram shows evolutionary relationships.

Background: Fossils, embryos, and body structures all provide evidence that organisms have changed over time. These same lines of evidence can also be combined to make inferences about evolutionary relationships among species. Recently, molecular evidence (DNA and proteins) has been used to confirm many of the evolutionary relationships (called phylogeny) determined by fossil, embryo, and body structure (morphology) evidence. The comparison of structures of different organisms is called comparative anatomy. Homologous structures are similar structures that related species have inherited from a common ancestor. Organisms with homologous structures might have evolved from the same ancestor. The more similar these structures are, the more closely related the organisms probably are. The same is true for molecular evidence. If two species have similar DNA and proteins, they probably evolved from the same ancestor, and the more similar the DNA or protein sequence is, the more closely related the two organisms most likely are.

Vocabulary: Evolution Comparative Anatomy

1 Minority Science Programs – School of Biological Sciences – University of California, Irvine Evolutionary Relationships 2009

Phylogeny Homologous Structures Morphology

Materials:  Images of several animal species  DNA sequences

Methods/Procedure: EVIDENCE FROM MORPHOLOGY 1. Compare images of several animal species and record your observations in TABLE 1. EVIDENCE FROM DNA SEQUENCES 1. Align the DNA segments from two animal species, and count the number of differences. 2. For each pair of species compared, write the number of differences in the proper space on TABLE 2. 3. Repeat steps 1-2 until you have compared all the species.

Name: ______Period: ____

Results:

TABLE 1 Body Structure Observations

Brown Bear

Polar Bear

Great Panda

Red Panda

Raccoon

TABLE 2 Polar Bear Great Panda Red Panda Raccoon Brown Bear Polar Bear Great Panda Red Panda Raccoon

Questions: 1. Which animals would you group together based on morphology? Why? ______2. According to your DNA sequence comparison, which 2 species appear to be the most closely related?

______3. Label the phylogenetic tree below according to similarities in DNA sequence.

4. What can body structures tell you about how species might be related? ______5. What does DNA tell you about how similar two species are? ______

Great Panda GTTAGTATAA

Red Panda GTCGATGAGA Polar Bear GCTCTCATAA

Brown Bear GATCTCATAA Raccoon GTCGATTCGA

5 Minority Science Programs – School of Biological Sciences – University of California, Irvine