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Mechanisms of Evolution Natural Selection Populations evolve, NOT individuals Gene pool - all alleles in a population s genes together (remember: alleles: alternative forms of a gene) Allelic frequency - % of any specific allele (p. 405 snapdragons) Genetic equilibrium - frequency of alleles remains same over generations = no evolution evolution.berkeley.edu/evosite/misconceps How does evolution happen? disrupting genetic equilibrium Mutations - caused by radiation or chemicals Genetic drift - alteration of allelic frequencies by chance events (random, affects small populations greater) Gene flow - Migration & Emigration Natural selection - allelic frequencies change due to nature selecting for advantageous variations ____________ selection - favors average phenotypes Spiders- larger spiders eaten by predators -Smaller spiders can t catch enough food -Favors _______ size Stabilizing, directional, and disruptive 1 BoardJennifer Wednesday, April 25, 2012 6:09:52 PM ET __________ selection - favors ONE extreme (on graph, selects to ____or ____) Woodpeckerslonger beaks eat more insects buried deep in bark (have more fitness) Long beaks favored Can lead to rapid evolution How do changes in gene pool lead to evolution? _____________ - when members of similar populations no longer interbreed to produce fertile offspring within natural environment _____________ isolation -physical barrier divides a population In an environment, medium-sized seeds become less common -Birds with smaller or larger beaks have easier time finding food = higher fitness Speciation rates - 2 hypotheses, both supported by fossil record ____________ - species originate through gradual change of adaptations; slow & steady ___________________- species originate quickly, in rapid bursts _____________ isolation - populations no longer mate and produce fertile offspring BoardJennifer Lava from volcanic eruptions, sea-level changes, rivers, mountains _________ selection - eliminates intermediate phenotypes Behavorial - different mating calls or seasons Different genetic material = fertilization won’t happen Polyploidy - having multiple chromosome sets Wednesday, April 25, 2012 6:09:52 PM ET 2 Patterns of evolution ____________ evolution - occurs when populations change as they adapt to different environmental conditions ___________________- ancestral species evolves into many new species to fit various niches Structural adaptations Body parts of an organism that help it survive Mimicry – more subtle Hawaiiian honeycreepers; Darwin’s finches ____________ evolution - unrelated species evolve similar traits because of similar environmental pressures *Adaptations: Evidence for Evolution Different cactus species around the world Ex. Teeth, claws, keen eyes, thorns, One harmless species looks a dangerous one Two or more harmful species look alike Harmless fly looks like a wasp; scarlet kingsnake looks like coral snake Yellow jackets, honeybees, many wasps use same coloring to say “Hey, stay away, I’ll hurt you!” _______________– enables species to blend in *_______________ adaptations Can happen very quickly Changes in an organism s metabolic processes Antibiotic-resistance bacteria (________) BoardJennifer Penicillin not as effective now Insects & weeds resistant to pesticides Wednesday, April 25, 2012 6:09:52 PM ET 3 *Evidence for evolution Fossils are aged by ___________ dating: using location of fossils in different layers of rock/soil to determine their age compared to where other fossils are located (___________ fossils in deepest layer) ___________ dating: measuring ½ life of radioactive isotopes of the element carbon (also called ________________ dating) _________ ______________ structures _______________ structures Structural *Indirect Evidence for Evolution Bird wing, butterfly wing Body part in present-day organism that no longer serves its original purpose (but was useful at some time) Our wisdom teeth, appendix, blind cave fish with eyes Embryology Embryo – earliest stage of growth & development of plants & animals Page 402 fig. 15.9: You had a tail and gills?? _______________ evidence Biochemical molecules: RNA, DNA, ATP, and many enzymes Compare amino acid sequences among organisms to see common ancestry Enzyme - cytochrome c - involved in cellular respiration BoardJennifer features (bones) indicate common ancestry http://evolution.berkeley.edu/evolibrary/article//evo_31 Vestigial structures Anatomy (p. 401 fig. 15.6) Body parts have similar function but NOT common ancestry accurate than relative dating *Anatomy cont. *Indirect evidence for evolution Wednesday, April 25, 2012 6:09:52 PM ET P.403 4