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Transcript
I. Early Earth and the origin of life A. Origin of the Universe (15 BYA) 1. Many theories exist 2. Most scientists favor the Big Bang Theory which state that the universe began as a dense concentration of matter smaller than a speck of dust which exploded outward violently Great Explanations of The Big Bang Theory appear in these books: B. Origin of the Sun (10 BYA) 1. Clouds of molecules, made of hydrogen gas, began to grow in mass which increased their gravity, which in turn, attracted more hydrogen to increase their mass 2. These clouds increased to such a huge mass, that it’s gravity smashed hydrogen molecules together, triggering a Fusion Reaction. We call these fusion reactions clouds Stars and one formed our Sun Relative Size of Inner Planets Relative Size Outer Planets Size of Planet Relative to the Sun Size of Sun Relative to Other Stars Our Sun Relative to the Largest Stars C. Origin of Earth 1. Clouds of matter caught in the Sun’s gravitational field began forming Planets 2. Solid matter collected into a dense core and radioactive decay melted the matter into a ball of molten rock that we call Earth Earth at Birth (4.5 BYA) 3. Conditions of Early Earth Prevented Life a) b) c) d) e) Tidal waves of Lava Poison gas atmosphere Deadly ultraviolet rays Constant meteorite bombardment Frequent earthquakes D. The Antiquity of Life 1. Life Appeared relatively early in Earth’s history a) Fossils of prokaryotes have been recovered from stromatolites that are 3.5 billion years old b) The oldest eukaryotes are 1.5 billion years old 2. Multicelled organisms arose 700 million years ago E. Spontaneous generation of Life: Abiogenesis 1. Abiogenesis is NOT evolution 2. Russian Biochemist Alexander Oparin introduced a plausible theory of chemical development of life in 1927 F. Origin of Life: Oparin/ Haldane Model 1. Abiotic synthesis and accumulation of small organic molecules: Amino Acids, Nucleotides and Sugars 2. The joining of monomers to form polymers 3. The formation of protobionts- groups of abiotically produced molecules able to maintain an internal environment 4. Origin of heritable Material A) DNARNAprotein model most likely evolved from a simpler model B) One hypothesis proposes RNA to be the first genetic material C) DNA was later favored due to its stability G. Evidence to Support the Oparin/Haldane Model 1. 2. Stanley Miller & Harold Urey constructed a primitive earth machine with methane, Ammonia, water vapor and hydrogen in the atmosphere which produced organic molecules Various experiments have produced all 20 amino acids, ATP, sugars, and DNA and RNA bases 3. Sidney Fox produced proteinoids: abiotically produced polypeptides a) Clay, hot sand and rocks can contain metals which will catalyze condensation reactions . b) Pyrite can provide a charged surface or free electrons to support bonding between molecules 4. When mixed with cool water, proteinoids self-assemble into Microspheres surrounded by a selectively permeable membrane 5. Coacervates form spontaneously from drops of polypeptides, nucleic acids and polysaccharides 6. RNA can base pair in the presence of zinc 7. RNA is autocatalytic- it can catalyze the formation of mRNA, tRNA, and r-RNA by itself 8. RNA fold is determined by its sequence a) This provides a mechanism for natural selection b) Stability and catalytic activity would be favored What does DNA and RNA polynucleotides with protein catalyzing chemical reaction in a lipid membrane sound like? A cell of course! But, scientists have only produced Coacervates in the lab DNA replication requires enzymes and DNA is required to make enzymes. Therefore, current theory suggests that the first genetic material was RNA because it can be auto catalytic (RNA could catalyze its own replication.) But, replication produces a complementary strand, not a coding strand, so two replications would be required. E. Origin of Eukaryotes 1. Autogenous Model- eukaryotes evolved by specialization of internal membranes derived from the prokaryotic plasma membrane a) Most endomembrane structures are believed to have differentiated from the plasma membrane invaginations b) Double membrane organelles (chloroplasts & mitochondria) may have involved secondary invaginations or more complex folding 2. Endosymbiotic Model- certain prokaryotic species called endosymbionts lived within prokaryotes a) Focuses mainly on chloroplasts and mitochondria b) Chloroplasts are thought to have descended from endosymbiotic photosynthesizing prokaryotes living in larger cells c) Mitochondria are postulated to be descendants of prokaryotic aerobic heterotrophs that may have been parasites or undigested prey of larger cells 3. Evidence for the Endosymbiont model a) Appropriate size to be descendants of eubacteria b) Replicate by splitting as do prokaryotes c) Contain their own DNA and ribosomes similar to prokaryotes d) Replicate independent of the cell II. Evidence of Evolution A. Fossil- any preserved remnants or impression left by an organism that lived in the past 1. Fossil Formation a) Some fossils are found as thin films pressed between layers of sandstone and shale and retain organic material b) Most fossils form from the mineral rich hard parts (bone, teeth, shells) because other substances decay rapidly c) Other fossils found by paleontologists are replicas, casts or molds left when corpses where covered by sand or mud 2. Limitation of the Fossil Record (Fossilization requires a series of improbable events) a) The organism must die at the right time in the right place in an anaerobic environment to avoid decaying b) Geological events must form the fossil and then the fossil must escape geological events such as erosion, pressure and heat c) Finally, the fossil must be found by someone who knows what they are doing 3. Ramifications of Fossilization: a) Most species never leave fossils b) Most formed fossils have probably been destroyed c) Only a small number of existing fossils have been found d) Therefore, the fossil record is composed of organisms that were widespread, abundant, lived a long time and had hard shells or skeletons 4. Fossil Dating a) Relative Dating 1) Younger strata is deposited on top of older 2) Strata from different sites can be correlated by similar fossils known as index fossils 3) Geologist have formulated a sequence of geologic periods by comparing many different sites b) Absolute Dating: Not errorless. +/- 10% 1) Radiocarbon Dating: uses C14 which has a half-life of 5730 years. Useful for dating organic matter less than 50,000 years old 2) K40 has a half life of 1.3 billion years old 3) Living organisms synthesize L-form amino acids which decay to D-form over time B. Biogeography- the geographical distribution of species 1. Islands with similar environments in different parts of the world are not populated by closely related species, but rather species related to organisms form the nearest main land 2. South American tropical mammals are more closely related to South American dessert animals than to African tropical animals 3. Australia has a diversity of marsupials in an environment that could easily support placentals C. Taxonomy- reflects the branching genealogy of the tree of life 1. Different taxonomic levels are related through descent from a common ancestor 2. Organisms thought to be closely related on the basis of anatomical features reveal common hereditary background D. Comparative Anatomy- Anatomical similarities between groups of the same taxonomic category show evidence of common descent 1. Forelimbs of mammals are Homologous Structures- structures that are similar due to descent from a common ancestor a) Although the limbs re used for different functions, it is obvious that the same skeletal elements are present b) It is logical then that the foreleg, wing, flipper or arm are similar due to a common ancestor 2. Vestigal Organs- rudimentary organs of little or no use to an organism that were valuable to the ancestral form. I.e. hip bones in snakes Homologous Bone Structures Similar structures found in different organisms suggests a common ancestry E. Comparative Embryology Closely related organisms go through similar stages in their embryonic development 1. All vertebrates (Fishes, Amphibians, reptiles, birds and mammals) go through an embryonic stage in which they posses gill slits on the sides of their throats a) As development progresses, gill slits develop into divergent structures, In humans, they form the Eustachian tubes that connect the middle ear and throat. b) Supports conclusion that all vertebrates descended from a common aquatic ancestor 2. Comparative embryology can often establish homology among structures that are so altered later in development that their common origins cant be determined by their fully developed forms F. Molecular Biology Organisms with similar proteins and DNA have similar ancestors 1. The closer two species are taxonomically, the higher the percentage of DNA they share 2. Even taxonomically distant organisms share some DNA and protein. This substantiates the idea that all life forms are related to some extent Examine the following DNA sequences. Which two of the three organisms is most closely related? Organism A: GGT CTC AAT GTA ATC CAA TCC AGG Organism B: GGT CAC ATT GTA ATG CAA TCG AGG Organism C: GGA CTC ATT GTA ATC CGG TCC AGC A & B Matches: 20 A & C Matches: 19 B & C Matches: 17 A & B are most closely related III. Mechanisms of Evolution Charles Darwin A. Natural Selection: Charles Darwin 1. All species have such a great potential fertility that their population size would increase exponentially if all individuals born would reproduce successfully 2. Most populations remain stable except for seasonal fluctuations 3. Natural Resources are limited a) Production of more individuals than the environment can hold leads to a struggle for resources b) Only a fraction of the original offspring survive 4. Individuals of a population vary extensively in character 5. Variation is due to random fertilization, independent assortment, crossing over, and mutation a) Survival is not random, but depends on the genes of the individual b) Organisms with favorable genes will live longer and have more offspring than those with average or poor genes c) Favorable genes will accumulate over generations B. Population Genetics 1. Individuals do not evolve. Therefore, populations must be studied. 2. Population- a group of interbreeding individuals of the same species that share a common geographic area 3. Gene Pool- total aggregate of all the genes in a population at any one time. Let’s fiddle around with some gene and genotypic frequencies Gene Pool 4. Hardy-Weinburg Theorem- Equations used to calculate gene and genotypic frequencies at genetic equilibrium. I.e. No evolution is occuring a) Gene Frequencies 1) Let P = the frequency of Dominant Genes in a population 2) Let q = the frequency of Recessive genes in a population 3) Therefore: P+q=1 All the dominant genes + all the recessive genes = all the genes b) Genotype Frequencies Hardy-Weinburg Notation 1) PP or P2 2) Pq + qP or 2Pq 3) qq or q2 Therefore: Genotypes Homozygous Dominant p Heterozygous q Homozygous Recessive p q P2 Pq qP q2 P2 + 2Pq + q2 =1 All the Homozygous Dominant + All the Heterozygotes + All the Homozyous Recessives = All the Population With these formulas, you can solve all Hardy-Weinburg problems c) Hardy-Weinburg Equilibrium will be maintained if the following conditions are met: 1) 2) 3) 4) 5) Infinitely large population size. This eliminates gene frequency change due to chance called Genetic Drift No immigration or emigration. Organisms entering or leaving the population changing gene frequencies called Gene Flow No differential rates of mutation. The rate at which A mutates to a is equal to the rate at which a mutates to A No mating preferences. The chances of any one genotype mating with another geneotype is equivalent to its frequency within the population No selection. All genes are neutral with each one having the same survival value C. Causes of Microevolution- the change in gene frequencies within a population 1. Genetic Drift- change in gene frequency due to random chance 2. Bottle Neck Effect- following a natural disaster, the small remaining population is unlikely to represent the genetic make up of the original population 3. Founders Effect- genetic drift that occurs when a few individuals colonize a new habitat Causes of Microevolution 4. Gene Flow-immigration or emigration of individuals disproportionately 5. Mutation- introduces new alleles into the population and immediately changes the gene pool 6. Non-Random Mating a) Individuals selecting mates that are geographically neighbors can lead to inbreeding b) Assortive Mating- individuals having a mating preference. 7. Natural Selection- a given phenotype is selected for (increasing gene frequency) or against (decreasing gene frequency) Ex. H. B. Kettlewell’s Experiment with the selection of moths by bird predators In England, before the industrial revolution, tree bark was a lighter color and lighter moths out numbered darker moths 9:1 Coal caused the tree bark to darken during the industrial revolution. The darker moths then numbered the lighter moths 9:1 Geospiza fortis Study by Peter and Rosemary Grant Antibiotic Resistant Strains of Bacteria are a Prime Example of Evolution IV. Speciation- The Development of New Species A. Types of Speciation 1. Anagenesis- the transformation of an unbranched linage enough to justify renaming it as a new species 2. Cladogenesis- the branching of one species into two or more species B. What is a Species? 1. Morphospecies- a species defined by anatomical feature 2. Biological Species- a group of individuals that can successfully interbreed and produce fertile offspring C. Reproductive Barriers Produce New Species 1. Prezygotic Barriers- prevent zygotes from forming a) Habitat Isolation- two species having different habitats in the same area b) Temporal Isolation- two species bread at different times of the day, season, or year c) Behavioral Isolation- two species don’t recognize the others behavior used to attract a mate d) Mechanical Isolation- anatomical incompatibility may prevent sperm transfer when closely related species attempt to mate e) Gametic Isolation- sperm from one species cannot fuse with the egg of another species 2. Post Zygotic Barriers- prevent the production of a viable, fertile offspring a) Hybrid Inviability- zygote fails to develop or an extremely frail offspring dies soon after birth b) Hybrid Sterility- hybrids are viable but sterile due to different number of structure of chromosomes c) Hybrid Breakdown- First generation is viable and fertile, but successive generations are feeble or sterile 3. Introgression- the transplantation of alleles between the gene pools of different species D. Biogeography of Speciation 1. Allopatric Speciation- occurs when a splinter population diverges in evolution from ist parent population after becoming geographically isolated a) Small populations are the best candidates because genetic drift and isolation can rapidly change a small gene pool b) Adaptive radiation- the emergence of numerous species from a common ancestor can be easily seen or island chains 2. Sympatric Speciation- New species forming without geographic isolation due to reproductive isolation a) Autopolyploid- a species arises when it doubles its previous chromosome number due to failure in meiosis b) Allopolyploid- a polyploid hybrid is formed from the contributions of two different species E. Genetic Mechanisms of Speciation 1. Speciation by divergence a) Two populations adapt to different environments and accumulate differences in genotype and phenotype b) Sexual Selection- can lead to reproductive barriers. According to the recognition concept of species, Natural selection would amplify adaptations that would enhance reproductive success 1) The adaptations may cause recognition problems 2) This can result in speciation . 2. Speciation by Peak Shifts a) Each adaptive peak is an equilibrium in which allelic frequencies maximize the average fitness of the populations members b) Environmental change may redefine the landscape, making new adaptive peaks possible c) Non adaptive shifts may destabilize a gene pool through genetic drift, bottle neck or founders effect and result in a new adaptive peak F. Gradual and Punctuated Speciation 1. Gradual speciation- occurs over a long period of time by the accumulation of microevolutionary change in the gene pool 2. Punctuated Speciation – new species arise quickly following its budding from its ancestral species and then stabilizes for a relatively long time V. Macroevolution- the origin of taxonomic groups higher than the species level. Macroevolution is concerned with major events in the history of life and the origin of new designs A. The Origin of Evolutionary Novelties 1. Preadaptations- a structure that evolved in one context and became co-opted for another function 2. Development and Macroevolution a) Changes in the rate or pattern of development can be due to small changes in regulatory genes, but can result in great morphological differences. I.e. Allometric growith b) Genetic changes that alter the timing of development may prevent structures from developing. Paedomorphosis is a condition where juvenile structures are found in the adult B. Difficulties in Interpreting Evolutionary Trends 1. A single correct evolutionary progression cannot be produced by the fossil record. I.e. Evolution of a horse 2. Evolution has produced many trends even if some branches go against the trends 3. Evolutionary trends may cease or reverse with changing conditions C. Continental Drift and Biogeography 1. Macroevolution has a dimension in space as well as time 2. Continental Drift has had a significant impact on the history of life by causing major geographic rearrangements affecting biogeography and evolution 3. The formation of the super continent Pangea and its subsequent break up can explain many cases of geographic distribution today D. Punctuations in the History of Biological Diversity 1. Major Adaptive Radiations a) Evolution of novel characteristics can open the way to new adaptive zones allowing many taxa to greatly diversify 1) A large increase in the diversity of sea animals occurred between the precambrian and paleozoic era 2) This occurred because bones and shells were developed allowing many groups to diversify greatly b) Empty adaptive zones can be exploited if the appropriate evolutionary novelties arise 1) Mammals existed for 75 million years before the first large adaptive radiation 2) Early in the cenozoic, mammals radiated out due to the ecological void created by the extinction of the dinosaurs 2. Mass Extinctions a) About 12 have occurred b) Mass extinctions profoundly effect the biodiversity by elimination of many species. But also allows other species to radiate out