In this lesson, students learn how modern-day scientists can take advantage of a tool not available in Darwin's time: molecular evidence. The discovery of the structure of DNA, and a greater understanding of genetics, have supported rather than refuted Darwin's ideas. Intense investigation by molecular biologists has uncovered genetic links between very diverse animal species, providing new evidence of common ancestry.
- Understand how genetics provides evidence of evolution
- Compare anatomical evidence with molecular evidence
- Understand the role of genetics in classification
- Two to three class periods
- Genetic Tool Kit QuickTime Video
- Animal Body Plans: Homeobox Genes PDF Document
- Molecular Connection Worksheet PDF Document
- Molecular Connection Answer Key PDF Document
- All in the Family Flash Interactive
- Evidence for Evolution HTML Document
- Molecular Clocks: Proteins That Evolve at Different Rates PDF Document
- The Common Genetic Code QuickTime Video
Before the Lesson
- Make copies of Molecular Connection handouts
Part I: Master Control Genes
1. Have your class watch the Genetic Tool Kit video, read the backgrounder, and take notes.
2. Then ask students to read the Animal Body Plans: Homeobox Genes handout and complete the activity.
3. Discuss the following questions:
- What are homeobox genes?
- What did Walter Gehring show with his experiment with theeyeless gene?
- How do homeobox genes provide evidence that all living things are descended from a common ancestor?
Part II: Molecular Connections
5. Next, introduce your students to cytochrome C--an enzyme found in virtually all organisms and needed for the release of energy from food. The Amino Acid Sequences in Cytochrome C chart on the Molecular Connections handout compares the amino acid sequences in this protein for several different animals. Have students infer how closely related the animals are based on the number of differences in their amino acid sequences. Then have students compare that data with a cladogram that has been constructed for those same animals based on their anatomical features. The cladogram provides independent confirmation of the animals' evolutionary relationships.
6. Ask groups to complete the handout. Point out that the bottom half of the Amino Acid Sequences in the Cytochrome C chart completes the data from the top half, so they need to look at both parts to answer the questions.
7. Discuss the answers in class.
Part III: Multiple Lines of Evidence
8. Have students visit the All in the Family Web activity to learn how multiple lines of evidence are used to figure out evolutionary relationships. Out of a group of three animals, students choose the two they think are most closely related. They can base their choice on appearance, anatomical similarities, developmental morphology, or molecular evidence. As they will discover, looks can sometimes be deceiving!
9. Ask students to use their biology textbooks to find two species to compare. Instruct them to write down how they think the animals are related and how they might find evidence to prove this relationship.
10. As a wrap-up to the the lessons on fossil and molecular evidence for evolution assign your students Evidence for Evolution. Divide the class into research teams of anatomists, molecular biologists, and paleontologists to search for structural, genetic, and fossil evidence for evolution. Direct the teams to selected online articles and Web sites, and tell them to report their findings to the class.
11. For extra credit, have students complete the Molecular Clocks: Proteins That Evolve at Different Rates worksheet. Point out that some proteins can tolerate a large amount of change and still carry out their function. Such proteins accumulate many mutations, and they can be used to help work out the evolutionary relationships between even closely related species. (This is a good supplement to the Molecular Connections activity.)
12. Alternatively, have students watch The Common Genetic Code video, which further illustrates the genetic similarity between all living things. The video highlights the research of scientist Paul Nurse, who demonstrated that a human gene could function in a lowly yeast.