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CHAPTER 25 CAMPBELL and REECE Slide 2 Conditions on early Earth made the Origin of Life possible Macroevolution : evolutionary change above the species level examples: 1. emergence of terrestrial vertebrates 2. mass extinctions impact on diversity of life 3. origin of key adaptations like flight in birds Slide 3 Where did 1st cell come from? 4 main stages could have produced very simple cells: 1. abiotic synthesis of small organic molecules 2. joining of these small molecules into macromolecules (proteins, nucleic acids) 3. packaging of these macromolecules into protocells, droplets with membranes that maintained internal chemistry different from their surroundings 4. origin of self-replicating molecules that eventually made inheritance possible Slide 4 Synthesis of Organic Cpds on early Earth Planets of our solar system formed ~ 4.6 billion yrs ago 1 st few hundred million yrs conditions would not have allowed life on Earth Slide 5 1 st Atmosphere Collisions would have vaporized any water preventing seas from forming Atmosphere thick with gases released from volcanic activity Slide 6 1st Atmosphere 1920s: Oparin (Russian) & Haldane (British) each came to conclusion early atmosphere was reducing environment (gain e-) in which organic cpds could have formed from simpler molecules Slide 7 1 st Organic Compounds Energy sources: Lightening Thermal energy Intense UV radiation Slide 8 Primordial Soup Haldane had hypothesized the early seas site of 1 st organic compounds 1 st cells Miller & Urey (Univ. of Chicago) in 1950s Tested Oparin & Haldane s premise Created reducing atmosphere Added cpds considered to have been there Slide 9 Miller & Ureys Experiment Slide 10 Miller & Ureys Results Slide 11 repeated using same or similar ingredients, different recipes for the atmosphere also produced organic compounds ?s about amounts of methane, ammonia (was there really enough to make it a reducing environment?) some repeated experiment in non-reducing, non- oxidizing conditions & still produce organic cpds Slide 12 Miller-Urey Experiment demonstrates: 1. Abiotic synthesis of organic molecules is possible under various assumptions about the composition of Earths early atmosphere 2. Meterorites may also have been source of minerals and organic molecules contain amino acids, lipids, simple sugars, uracil Slide 13 Murchison Meteorite Slide 14 fell in so named town in Australia in 1969 large (100 kg) and was quickly retrieved 2010 article published in Scientific American: results of mass spectrometry (separating cpds based on charge & size) have revealed at least 14,000 unique molecules Slide 15 Abiotic Synthesis of Macromolecules 2009 study showed the abiotic synthesis of RNA monomers can occur spontaneously from simpler precursor molecules drip solutions with amino acids (aa) or RNA nucleotides onto hot sand, rock, or clay polymers of aa & RNA (w/out using enzymes or ribosomes) Slide 16 Protocells Basic characteristics of life : reproduction & metabolism: 1 st cells would have had to be able to reproduce which would have required them to have a source of nitrogenous bases, sugars, phosphate groups now complex enzymes make this all happen Slide 17 Vesicles as 1 st step? When lipids & other organic molecules added to water vesicles spontaneously form lipid bilayer (separation of hydrophiloic & hydrophobic molecules) these abiotically produced vesicles reproduce and grow on their own. clay like from early Earth will be absorbed into the vesicles some vesicles demonstrate semi- permeability Slide 18 Self-Replicating RNA RNA can act as enzyme RNA catalysts called: ribozymes some can make complimentary strands of short pieces of RNA mutations more stable &/or successful Slide 19 Ribozyme once self-replicating RNA possible, much easier for further changes to happen. once double-stranded DNA appeared it would have been more stable so RNA left with role we see today Slide 20 The Fossil Record Documents the History of Life Slide 21 The Fossil Record based mostly on sequence in which fossils have accumulated in sedimentary rock strata an incomplete record of evolutionary change (gaps still be filled in) known fossil record biased toward species that: survived for long periods of time were abundant were widespread in certain types of environments made of some hard parts Slide 22 This could mess up the fossil record, you know. Slide 23 Tiktaalik extinct closest relative to of 1 st vertebrate to walk on land Slide 24 Slide 25 Radiometric Dating ethod of absolute dating based on decay of radioactive isotopes (1 element different element + some particle) half-life = rate of decay of the specimen lives are constant & characteristic to each radioactive element outside conditions do not affect rate of decay Slide 26 Dating Fossils C-14 in all living things C-14 decays into N-14 life = 5,730 years measure ratio of C-12 to C-14 left in fossil can only use C-14 dating up to about 75,000 yrs old amt of C-14 left after that so minimal that accuracy becomes an issue if organism dead Cretaceous Mass Extinction ~65.5 million yrs ago between Mezozoic & Cenozoic eras >50% all marine life extinct eliminated all dinosaurs (except birds) Reason? Thin layer of clay enriched in iridium lies between sedimentary rock from the 2 eras. Iridium very rare on Earth but common in meteorites Slide 74 Cretaceaous Mass Extinction Chicxulub Crater off Yucatan penisula is a 65 million year old scar that could have been caused by hit from a comet or asteroid (crater size indicates hit by something 10 km in diameter) Slide 75 6 th Mass Extinction ? Typical background rate for extinctions is considered to be 1 10 in 400 yrs. There have been > 1,000 extinctions in past 400 yrs Not counting those species (probably some in rain forests) that are becoming extinct that we had never discovered Losses to date have not reached those of the BIG 5 Slide 76 Consequences of Mass Extinctions significant & long term effects extinct species is gone forever course of evolution is changed takes at least 5-10 million yrs for diversity to recover from a mass extinction Slide 77 Mass Extinctions & Ecology Slide 78 Adaptive Radiations Fossil record tells us diversity of life has increased over past 250 million yrs increase largely due to adaptive radiation: periods of evolutionary change in which groups of organisms form many new species to fill different niches Large scale adaptive radiations occurred after each of BIG 5 Slide 79 Radiation of Mammals when land dinosaurs became extinct 65.5 million yrs ago mammals moved in and filled the ecological roles or niches now available to them original mammals 180 million yrs ago but they remained small, not very diverse, mostly nocturnal, Slide 80 Development Genes Genes that control development influence the: rate & timing spatial pattern of change in an organisms form as it develops from zygote adult Slide 81 Change in Rate & Timing Heterochrony : (Gr: different, time)an evolutionary change in the rate & timing of developmental events Humans relative shape due in part to relative growth rates of different body parts during development Slide 82 Relative Skull Growth Rates Humans have mutation that slowed growth of jaw relative to other parts of skull produced an adult that looks more similar to chimp fetus than chimp adult Slide 83 Paedomorphosis Adults of some species retain juvenile features of ancestors example: marine salamander axolotl Slide 84 Changes in Spatial Pattern homeotic genes: master regulatory genes that control placement & spatial organization of body parts in animals Slide 85 Hox Genes 1 class of homeotic genes provide positional information in animal embryo Slide 86 Evolution of Development Origin of novel morphological forms likely due to new developmental genes arising from gene duplication events Insects have crustacean-like ancestors that all have more legs .the Ubx gene is expressed in main trunk of body; in insects it is expressed in abdomen.in crustacean legs .in insects it suppresses leg formation Slide 87 Ubx Gene mutation Crustacean Body Insect Body Slide 88 Changes in Gene Regulation Harmful Changes can be limited to single cell type may have fewer harmful side effects than point mutations .so less likely to be a lethal change Marine Stickle back Fish Lake Stickleback Fish Slide 89 Evolution is not Goal Oriented new forms arise by slightly modifying existing forms novel & complex structures can arise as gradual modifications of ancestral structures each step in process of evolving into something complex would have been useful to the species Slide 90 Ranges of Eye Complexity among Molluscs Slide 91 Evolutionary Trends Species Selection Model proposed by Steven Stanley thinks of species as individuals: speciation is their birth, extinction their death new species that diverge from them are their offspring. species that last the longest & generate the most new species determine the direction of major evolutionary trends. Slide 92 Species Selection Model Slide 93 Evolutionary Trends Natural Selection still plays a role example: ancestors to modern horse were browsers until mid-Cenozoic when grasslands spread across large areas. Horses that were grazers and able to run fastest from predators were selected for Slide 94