What kind of evidence do scientists use to determine evolutionary relationships?
Activity Summary Learning Objectives
Suggested Time
Background As explained in the NOVA scienceNOW segment, FOXP2 also plays a role in the processes involved in human speech and birdsong: people with an altered form of the gene have difficulty with many aspects of speech, and birds whose FOXP2 activity is disrupted have trouble learning songs. Despite these and other observations, scientists still don't know which other genes FOXP2 regulates or what its function is in the numerous other species that share this gene with birds and humans. That FOXP2 is so widespread raises additional questions, not only about its role in other organisms, but also how the gene differs from one organism to the next. All life on Earth arose from a single common ancestor, and our genes reflect this shared ancestry. As species differentiated over evolutionary time, the DNA sequences in their genes acquired slight changes. According to evolutionary theory, these changes accumulate over time: species that diverged from each other long ago have more differences in their DNA than species that diverged recently. Scientists use this degree of difference as a molecular clock to help them predict how long ago species split apart from one another. In general, scientists say the longer ago two species split, the more distantly related they are. You may need to remind your students about the nature of DNA, genes, proteins, and amino acids and how they differ from one another. DNA is a molecule made up of four types of units called bases. The four bases—adenine (A), cytosine (C), guanine (G) and thymine (T)—collectively make up the DNA "alphabet." Genes are distinct locations along the length of a DNA molecule. The sequence of bases in a gene determines the order of amino acids in a protein, and the order of amino acids acts as the blueprint for protein assembly. Because the DNA sequence determines a protein's amino acid sequence, a gene shared by two closely related organisms should have similar, or even identical, amino acid sequences. That's because closely related species most likely diverged from one another fairly recently in the evolutionary span. Thus, they haven't had as much time to accumulate random mutations in their genetic codes. For years, scientists have used DNA and amino acid sequences to decipher relationships between closely related species, such as different types of reptiles, birds, and even bacteria. The approach, called "molecular phylogeny," compares sequence data and ranks organisms' degree of relatedness based on the differences in their DNA. As researchers sequence the genomes of an increasing number of organisms every year, they uncover more data to use in evolutionary studies. In the emerging field of phylogenomics, researchers simultaneously compare numerous genes—and will one day compare complete genomes—to build new evolutionary trees. In this activity, your students will analyze a suite of amino acid sequences from a gene that makes the protein Cytochrome C. All eukaryotic organisms share this protein, which plays a central role in the energy-producing process of cellular respiration. Cytochrome C is an iron-containing molecule that carries electrons during the electron transport chain in cellular respiration. The protein is found in many lineages, including those of animals, plants, and numerous unicellular species. Its ubiquity makes it a convenient tool for studying evolution. By counting the number of amino acid differences between humans and six other species, your students will be able to make predictions about how closely related humans are to each species. Before the Lesson
Divide the class into four teams. Assign each team one of the following genes: FOXP2, hemoglobin alpha, eyeless, and sonic hedgehog. Have students visit the Kyoto Encyclopedia of Genes and Genomes and look up their gene's amino acid sequence in humans. Have students research how many of the six species from their handouts share this gene with humans; for all cases in which species share the gene, have students write down the first ten amino acids listed in the database. Then have students prepare a short report about the gene, how much similarity they discovered between humans and other species, and what scientists know about the gene's function. ASSESSMENT Student Handout Questions
Use the following rubric to assess each team's work.
The "Bird Brains" activity aligns with the following National Science Education Standards (see books.nap.edu/html/nses). Grades 9-12
Content
Standard F
Classroom Activity Author Jennifer Cutraro and WGBH Educational Outreach Staff Jennifer Cutraro has 12 years of experience in science writing and education. She has written text and ancillaries for Houghton Mifflin, K12, and Delta Education and has taught science and environmental education at science centers across the country. She also contributes news and feature stories about science and health to media outlets including The Los Angeles Times, The Boston Globe, Science News for Kids and Scholastic Science World.
What types of evidence are used to determine evolutionary relationships?Evidence for evolution comes from many different areas of biology:. Anatomy. Species may share similar physical features because the feature was present in a common ancestor (homologous structures).. Molecular biology. DNA and the genetic code reflect the shared ancestry of life. ... . Biogeography. ... . Fossils. ... . Direct observation.. What are 3 main types of evidence of evolution?Evidence for Evolution. Ancient Organism Remains.. Fossil Layers.. Similarities Among Living Organisms.. Similarities of Embryos.. What are the 5 evidences of evolution?There are five lines of evidence that support evolution: the fossil record, biogeography, comparative anatomy, comparative embryology, and molecular biology.
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