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TAMU BIOL 112 - CH25 (2nd Half)

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Chapter 25 The History of Life (2nd Half of Ch)Macroevolution is the major change in life above the species level in earth’s history- The evolution of new major groups and new structures- Extinction and adaptive radiation- Revealed in the fossil recordFig 25.4Origin of new groups (amphibians, birds, squirrels)- Starts with microevolution which leads to speciation- 1 new species is the ancestor of the entire groupo Ch 22 elephant family exampleAdaptive Radiation- Diversification from an ancestoro New adaptation of ancestral species lead to expansion of the rangeo Moving into new areas and habitats promoted more speciation- Historically, adaptive radiation followed after mass extinctionso Opened new areas and resources- Also seen in isolated island groups- Many branches were lost over time as environments changed (horses)Origin of new features- By incremental evolutiono Each step is better adapted for the same use (eyes in mollusks)- Exaptation occurs when an existing adaptation is modified for a different useo Ex- Hair (insulation) led to porcupine quillso Ex- Hinge bones in mammalian ancestors become ear bones (25.6 and CH34)o Ex- Feathers (insulation) led to flight- Effects of developmental genes (evodevo)o Their function is to turn genes on and off at precise times and places during developmento Homeotic genes are genes that control the placement of body parts Mutation in one or two of the genes causes massive effects (18.20) Hox genes- 25.23-24- Heterochrony is the change in the rate or timing of developmental eventso May produce new final shapes (chimps and humans)o May produce a sexually mature adult with juvenile features (PAEDOMORPHIS) (salamander with


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TAMU BIOL 112 - CH25 (2nd Half)

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