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Transcript
EVOLUTION Date: evolution: Δ over time process by which modern organisms have descended from others theory: well-supported, testable explanation for natural phenomena 15-3: Darwin presents his case (p.378) *On the Origin of Species published in 1859 Darwin observed variation in nature & on farms o genetic (inherited) variation – differences passed from parents to offspring o artificial selection – humans breed organisms w/ desired traits (fig.15-10) * Natural Selection struggle for existence – organisms compete to obtain food, living space, other necessities fitness – ability to survive & reproduce in a specific env results from adaptations – inherited characteristics that ↑ chance of survival can be anatomical (structure), physiological (fxn), or behavioral survival of the fittest – ind better suited to their env survive & repr. most successfully natural selection – results in Δ’s in inherited characteristics of a population, ↑’ing fitness of a species (spp) in its env after many generations common descent – all spp were derived from common ancestors Date: *Evidence of Evolution (p.382) A. Fossil Record o Fossils: preserved remains of ancient organisms B. geographic distribution of spp C. homologous structures: dif mature forms but develop from the same embryonic tissues (fig 15-15) o showed common descent of 4-limbed vertebrates o vestigial organs – serve no useful function unaffected by natural selection D. comparing DNA E. similarities in embryology (fig 15-17) o groups of embryonic cells develop in same order & patterns homologous structures! Evolution: “the grand unifying theory of the life sciences” Date: 16-1: Genetic Variation (p.393) ↑’s chance that some members of spp survive Δ’s in env. studied in populations – group of individuals of same spp gene pool: all genes/alleles in a pop. relative frequency: # of times an allele occurs in a gene pool compared to other alleles for same gene (fig 16-2) evolution is any Δ in relative frequency of alleles in a pop. 2 sources: 1. mutations – any Δ in DNA sequence result from (a) mistakes in DNA replication or (b) chemicals/radiation can be “silent” – do not Δ AA no effect on phenotype 2. gene shuffling (sexual reproduction) does NOT affect allele frequencies Date: 16-2: Evolution as Genetic Change (p.397) * natural selection NEVER acts directly on genes; only organisms (phenotype not genotype!) NS on single-gene traits (fig 16-5) can lead to Δ’s in allele frequencies NS on polygenic traits (controlled by >1 gene) 1. directional selection – occurs when ind. at 1 end of bell curve have higher fitness than those in middle or other end (fig 16-6) 2. stabilizing selection – ind. near center of curve have highest fitness (fig 16-7) 3. disruptive selection – ind. at upper & lower ends of curve have highest fitness (fig 16-8) can cause split into 2 distinct phenotypes genetic drift – random Δ in allele freq. can reduce genetic variation (fig founder effect – migration of some members of pop. Date: 16-3: Speciation (p.404) * speciation: formation of a new spp if a genetic Δ in 1 ind. ↑’s fitness, allele will eventually be found in many ind. diversity of spp ↑’s chance that some organisms survive major Δ’s in env * reproductive isolation – occurs when 2 pop. no longer interbreed separate gene pools form speciation develops from: 1. behavioral isolation –2 pop. have differences in reproductive strategies 2. geographic isolation – 2 areas are separated by geographic barriers (rivers, mount, lakes, etc) 3. temporal isolation – 2 or more spp reproduce at dif times Date: 17-1: The Fossil Record (p.417) Interpreting Fossils 1. relative dating –compare placement w/ fossils in other rock layers younger layers are above older layers index fossils – easily recognized spp that existed for short time but over wide geographic range 2. radioactive dating – use of half-lives to determine absolute age of rocks (fig 17-4) half-life: length of time for ½ of radioactive atoms in a sample to decay Geologic Time Scale – organized by age of rock layers where major Δ’s in fossils occurred (fig 17-5) time btwn Precambrian & present divided into 3 eras: 1. Paleozoic 2. Mesozoic 3. Cenozoic (most recent) Eras are divided into periods Date: 17-3: Evolution of Multicellular Life *88% of Earth’s history was during Precambrian 1st organisms were prokaryotic Paleozoic Era o “Cambrian Explosion” – great diversification of life forms o Permian mass extinction 95% of complex ocean life disappeared Mesozoic – age of reptiles o Cretaceous mass extinction (dinosaurs, ½ of all plant & animal groups) Cenozoic – age of mammals Date: 17-4: Patterns of Evolution *macroevolution: large-scale evolutionary patterns & processes that occur over long periods of time extinction o 99.99% of spp that ever lived are extinct o mass extinctions opened new habitats & added ecological opportunities rapid evolution adaptive radiation – single spp evolves into diverse forms that live differently convergent evolution – unrelated organisms come to resemble one another (fig 17-23) coevolution – 2 spp evolve in response to Δ’s in each other o flowering plants & insects genes o hox genes – guide development of major body structures in animals