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Warm-Up 5/18/2010 • Why are transitional fossils important evidence for evolution? • Give two examples of transitional fossils -Take out 17.1 + 454-455 Notes to be stamped Evidence for Evolution Body Structures, Embryos, DNA/RNA Comparisons Homologous Structures • Structures with different mature forms but come from same embryonic tissues • Best seen in animals with backbones • Ex: humans, cats, whales, and bats all have same basic bones in their limbs • Evidence that all four-limbed animals with backbones descended (with adaptations) from common ancestor Homologous Structures Vestigial Structures • Some organisms have traces of homologous structures that they no longer use • Ex: human tailbone, human appendix, snake leg buds Comparative Embryology Embryos of diverse organisms look very similar! Comparative Embryology • Shows that same groups of embryonic cells develop in same order and in same patterns to produce organs, etc. • Groups of cells produce homologous structures Snapping Turtle Embryo Cat Embryo DNA/RNA Comparisons • Genetic similarities between organisms help scientists determine correct phylogenetic trees ▫ How closely related organisms are ▫ Who evolved from who, even when physical similarities aren’t obvious Afr. Vulture Am. Vulture Stork Types of Evidence from DNA/RNA • Highly related organisms share a high percentage of DNA in common ▫ Humans and chimps share 96% of DNA in common ▫ About 40 million differences in 3 billion nucleotides ▫ Only 2,000 of these differences code for something (Emory University, 2005) Types of Evidence from DNA/RNA • Seemingly unrelated organisms share genes that code for the same proteins ▫ Humans and yeast both have the gene that produces the protein myosin ▫ Myosin is used in human muscle tissue ▫ Myosin in yeast helps organelles move “Molecular Clocks” • The number of mutations found in DNA can help us estimate the length of time between the evolution of two organisms ▫ Mutations accumulate at a constant rate ▫ The more differences between two organisms, the longer apart they evolved from each other Human/Chimp Chromosome Activity • Read Background and Answer a, b, c (p. 1) • Do Chromosome Analysis #1-9 (p. 1, 2) • Comparison of Human/Chimp Chromosomes: Do 1, 2 and Answer 3 a-g