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Bio1_23_EvolutionIII - 1 2 3 1 2 4 5 1 2 6 7 Self-Quiz 1...

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1 Self-Quiz 1. What is directional selection? Disruptive selection? Stabilizing selection? 2. How can sexual selection lead to dimorphic sexes? 3. What role does the environment play in maintaining diversity? 4. Describe prezygotic & postzygotic reproductive isolating mechanisms. 5. Give examples of adaptive radiation. Overview Ch. 17: Macroevolution – The Burgess Shale – Principles of macroevolution Ch. 18: History of Life – Section 18.2: Fossil record The Burgess Shale Marine life ~ 540 mya – Cambrian explosion – Highly diverse Ancestors of all modern animal groups Macroevolution Evolution at higher levels of classification – Gradualistic model: slow change over time •Isolation & independent, gradual evolutionary pathways with many transitional links – Punctuated equilibrium model: rapid change •Periods of no change interrupted by speciation •Transitional links less likely to be found – Both models used in interpreting fossil record •Remember “sudden” = many thousands of years Macroevolution Gradualistic model Punctuated equilibrium model Developmental Genes Gene expression & development – All animals share the same control switches for development Pax6: eye development Tbx5: limb development in mammals & birds Hox: number & appearance of repeated structures Diversification & Extinction Patterns of macroevolution – Speciation, diversification, & extinction E.g., evolution of the horse – Trends: size, toes, ∆ in tooth size & shape – Adaptive radiations 35 mya & 15 mya
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