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Test Biology Notes Evolution.doc

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University of Toronto St. George
Spencer Barrett

Ilana Tavshunsky (M4 Biology) – Dr. Nino TEST BIOLOGY – EVOLUTION TEXTBOOK NOTES: LIFE IN THE UNIVERSE: - Need for life: 1. Source of Energy 2. Carbon 3. Liquid water - 4 billion years ago – interstellar dust cloud collapsed into swirling accretion disk which gave rise to sun & planets - Fragile complex organic molecules survived heat of solar system formation by sticking together in comets on edge of disk (temp. = freezing) - Comets & other cloud remnants carried molecules to Earth How Organic Molecules Might Form in Space: - Interstellar ice forms when molecules like methanol, water, hydrocarbon freeze onto granules of silicate in interstellar clouds - Ultraviolet radiation from nearby stars breaks some chemical bonds in frozen compounds - Broken down molecules recombine into complex compounds (e.g. quinines, nitriles, ethers, alcohols) which would not form if fragments could float away Organic Molecules Found in Space: - Organic molecules found in carbon-rich meteorites - Six-carbon molecule (HTM) also created → known to create amino acids in warm, acidic water Notes from Questions: - Molecules from space that naturally form capsule-like droplets in water could have provided enclosure (similar to plasma membrane) for prebiotic molecules - Scientists know about existence of complex organic molecules in space from spectral analysis of light received from stars + examination of meteorites THE ORIGIN OF LIFE ON EARTH: - Recently discovered → prebiotic conditions on other planets and their moons - Peptides and nucleic acids may form polymers in conditions thought to have existed in primitive terrestrial environment - RNA capable of self-replication - Exobiology → study of life in regions beyond our planet Steps in Origin of Life: 1. Formation of Earth (4600 mya) + volatile organic chemicals come from collision comets & meteorites → precursors of biochemical molecules 2. Prebiotic synthesis and accumulation of organic molecules 3. Prebiotic condensation reactions involving synthesis of polymers & peptides (proteins) and nucleic acids (probably only RNA) with self-replicating and catalytic (enzymatic) abilities 4. Synthesis of lipids – which assemble into double layered membranes, and liposomes, and capturing of prebiotic (self replicating and catalytic molecules) within boundaries. 5. Formation of probiont → precursor to first living systems Scenarios for the Origin of Life: Ocean Surface (Tidal Pools) Life arose in tidepool, pond, or moist clay in primeval Earth. Gases from volcanoes energized by UV light or lightning to form prebiotic molecules in froth Panspermia (Cosmic Ancestry) Living organisms seeded on Earth from comets/meteorites → organisms would have had to survive heat of entry Undersea Thermal Vents Recently proposed → life arose from smokers (ancient volcanic vents) → environment provides necessary gases, energy, sources of catalysts Notes from Questions: - Ribozymes can act both as genes and enzymes → origin of life could be because RNA molecules could perform necessary catalytic activity to assemble themselves → once formed can synthesize proteins - Enzymes cannot be formed without genes and genes cannot be formed without enzymes → why RNA, with its dual function, is important PREBIOTIC EXPERIMENTS: Ilana Tavshunsky (M4 Biology) – Dr. Nino - Early atmosphere may have been similar to vapours given off my modern volcanoes (CO2 CO 2 N , no oxygen) - Iron pyrite (fool’s gold) may have been possible stabilizing surface for synthesis of organic compounds - Organic compounds more stable in colder temperatures and can make a lattice in ice The Origin of Eukaryotic Cells: - First firm evidence of eukaryotic cells 540-600 mya - Believed to have evolved from large prokaryotic cells that ingested other prokaryotes → formed symbiotic relationship with engulfed cells (endosymbiosis) For Example: 1. Mitochondria – aerobic respiration (engulfed Aerobic bacterium – present day aerobic bacteria) 2. Chloroplast – photosynthesis (engulfed photosynthetic prokaryote) - Animal cells may have evolved from plant cells that lost their chloroplasts THE HISTORY OF LIFE ON EARTH: - Explanation of origin of life based on fossil record and genetic comparison of modern life forms - Modern life forms arose from ancient ancestors that have become extinct (were present ~ 3500 mya) - Life evolved beyond the simple cell stage only ~ 600 mya → probably because needed other things (e.g. buildup of free oxygen in atmosphere – byproduct of photosynthesis) Notes from Questions: - Build up of free oxygen important → animal cells use aerobic respiration and need free oxygen to carry out metabolic processes → complex animals = higher oxygen demand - Appearances: 1. Invertebrates – 550 mya 4. Retiles – 265 mya 2. Fish (ray-finned) – 400 mya 5. Mammals – 205 mya 3. Land plants – 375 mya 6. Birds – 185 mya - Mass extinctions result from the vacation of many niches → survivors undergo adaptive radiation and diversify – occupy vacated niches - The first diversity was chemical diversity FOSSIL FORMATION: - A fossil may be preserved remains of organism, impression of it in sediment (cast), or marks made by it during lifetime (trace fossils) - For fossilation need rapid burial of organism (usually in water-borne sediment, normal processes of decay must be stopped permanently (remains isolated from air, water, and decomposing microbes) Modes of Preservation: - Silication (or petrification) → silica from volcanic ash slowly incorporated into partly decayed wood - Phosphatisation → bones and teeth preserved in phosphate deposits - Pyritisation → Iron pyrite replaces hard remains of organism - Tar pit → animals fall into/trapped mixture tar/sand - Amber → gurn from conifers traps insect and hardens - Limestone → Calcium carbonate from remains of marine plankton deposited as sediment that traps remains of other sea creatures. Transitional Fossils: - Mixture of traits found in two different but related taxonomic groups - Suggest one group gave rise to another Notes from Questions: - Decay must be stopped for fossilization THE FOSSIL RECORD: - Fossils are remains or impressions of plants/animals trapped in sediments after death - Layers of sedimentary rock arranged in order deposited (most recent top layers) unless disturbed Profile With Sedimentary Rocks Containing Fossils: - New fossil types = change in environment → drastic environmental changes + appearance new niches = new types of organisms dominate - Rate of evolution can vary → bursts of species formation vs. stability of species (stasis) Notes from Questions: - Radiometric dating can be used to determine how old something is Ilana Tavshunsky (M4 Biology) – Dr. Nino DATING FOSSILS: - Rarely able to be dated directly (generally rocks they are found in dated) - Exception is radiocarbon dating – directly measures - Dating methods can be divided into two categories: 1. Rely on gradual radioactive decay of an element (e.g. radiocarbon, potassium-argon, fission track) 2. Other methods (e.g. tree rings, palaeomagnetism) DNA HYBRIDISATION: - More closely species related = fewer differences in exact sequence of bases (less time for point mutations) - If modern species compared to see how long ago shared common ancestor, can measure relatedness and can be calibrated with fossil dates to create a molecular clock DNA Hybridization: 1. Blood samples taken & DNA isolated 2. DNA made to unwind using heat 3. Enzymes used to snip single strands DNA into smaller pieces 4. Segments of species combined to see how closely bind to each other (single strands will attempt to find complementary segments and rewind into double helix) 5. Greater similarity = greater attraction between strands = harder to separate → measuring how hard to separate can get crude DNA relatedness 6. Degree similarity can be found by finding temperature separates IMMUNOLOGICAL STUDIES: - Provide method indirectly finding degree of similarity of proteins of different species - Differences in proteins = differences in DNA that codes for them Method for Immunological Comparison: 1. Blood serum (containing blood proteins but no cells) collected from one species and injected into other → causes formation of antibodies in this species’ blood → identify proteins, attach to them, render harmless 2. Sample of blood in second species taken & antibodies extracted 3. Antibodies added to blood samples other species → the more sample is similar to first species’ blood, the greater reaction (forms precipitate) OTHER EVIDENCE FOR EVOLUTION: - Amino Acid Sequences o Each protein has specific number of amino acids arranged in specific order o Differences in sequence reflect changes in DNA sequence o Hemoglobin beta chain standard molecule for comparing precise sequence of amino acids in different species - Comparative Embryology o If compare embryos of different species → notice animals more similar in earlier stages embryonic development o Ernst Haeckel proposed principle: ontogeny recapitulates phylogeny → the development of an individual (ontogeny) retraces stages individual species passed in evolution (phylogeny) – now know this is oversimplified + misleading Notes from Questions: - Comparative embryology contributes evidence to support the concept of evolution because animals that share closer evolutionary relationships have similar embryonic development to a later stage - Commonly used biochemical methods for precisely analyzing genes in organisms to determine evolutionary relationships: DNA profiling & DNA sequencing, etc. → based on assumption more closely related organisms have more similar DNA THE EVOLUTION OF NOVEL FORMS: - New field of evolutionary developmental biology (evo-devo) addresses origin and evolution of embryonic development & looks how modifications in developmental processes lead to new features - Hox genes → genes that control animal development → highly conserved (show few changes in different lineages) - Hox genes are present in practically all animals and control development of front and back parts The Evolution of Novel Forms: - Tiny changes in Hox genes can have huge effect on morphology → almost certainly were important in evolution of novel structures and body plans - Principles of evo-devo: o Evolution works with what is present (new structures = modifications pre-existing structures Ilana Tavshunsky (M4 Biology) – Dr. Nino o Functional redundancy in part of a multifunctional structure → specialization & division of labour → two new structures develop o Modular architecture in animals allows for modification/specialization of body parts + genetic switches allow changes in one part of structure independently from other parts Shifting Hox Expression: - Huge diversity can arise through small changes in genes controlling development COMPARATIVE ANATOMY (same as page 78!!!): - Evolutionary relationships between groups of organisms determined mainly by structural similarities → homologous structures (homologies) - Homologous → similar bones arranged in a similar pattern → indicative of common ancestry Notes on Questions: - Homology in behavior of animals is sometimes used to indicate relatedness - Genetically determined behavior is inherited in the same way as structural features VESTIGIAL ORGANS: - Reliable indicators of common ancestry - The less a part of an animal is used for a specialized purpose, the more important it is for classification - Easy to detect if feature unaffected by adaptations - Vestigial organs have no clear function and are no longer subject to natural selection - Sometimes vestigial organs can have a small function → still vestigial if minor & unrelated to original function Notes on Question: - When an organism gets new niche/habitat/way of doing something, some structure may hinder more than help it in its new way of life - The organ may regress over time because little energy will be put in a little used structure - The organ may not disappear altogether because the genes that code for it are still there → but if accumulation of mutations sufficient, may cause switching off of relevant genes - Can see gradual reduction in size of vestigial organ as progresses through ancestor, transitional forms, modern forms BIOGEOGRAPHICAL EVIDENCE: - Biogeography → study of geographical distribution of species (present-day and extinct) - Biogeography stresses the role of dispersal of species from a point of origin across preexisting barriers - Flora and fauna on different islands more closely related to adjacent continental species than to each other OCEANIC ISLAND COLONISERS: - Oceanic islands have unique biota → certain groups plants/animals able to colonize them while others can’t - Animals reach → marine habit or can survive long periods in sea/air - Plants reach → few fruits/seeds salt tolerant, often transferred by wind/migrated birds CONTINENTAL DRIFT AND EVOLUTION: - Movements up to 2-11 cm per year - Earth has 12 major crustal plates driven by thermal convection currents in mantle → geographical process known as plate tectonics - Modern continents once joined together as “supercontinents” (e.g. Gondwana) GENES AND EVOLUTION: - Different gene combinations → due to shuffling of chromosomes during gamete formation - New allele combinations → mate selection & chance meeting of vast range different gametes from 2 parents - Organisms with inferior collections of genes → reduced reproductive success → genes they carry will decrease in frequency in next generation’s gene pool - Organisms with more successful combination of genes → higher reproductive success → genes increase in frequency in gene pool Notes on questions: - Variation = raw material on which natural selection acts - Selection acts on phenotype (result of genotype & environment) ADAPTATIONS AND FITNESS: - Adaptation → any heritable trait (structural, physiological, behavioral) that suits an organism to its natural function in environment (its niche) Ilana Tavshunsky (M4 Biology) – Dr. Nino - Fitness → ability of organism to maximize the number of offspring surviving to reproductive age - Physiological adjustment (acclimatization) → organism’s ability to adjust during lifetime to changing environmental conditions (e.g. person’s acclimatization to altitude) Notes on questions: - Adaptive value of larger body size at high latitude → large body size conserves more heat → more heat producing mass relative to surface area over which heat is lost THE MODERN THEORY OF EVOLUTION: - Charles Darwin credited with development of theory of evolution by natural selection - Some aspects of his theory (e.g. mechanism of inheritance) were problematic → now explained - New synthesis → currently accepted model - Neo-Darwinism: refined version of Darwin’s theory using modern biological knowledge (especially genetics) DARWIN’S THEORY: - 1859 → Darwin and Wallace jointly proposed new species could develop by process of natural selection - Natural selection → mechanism by which better adapted organisms survive to produce a greater number of viable offspring (making them more common in population) - Darwin could not explain origin of variation or mechanism for its transmission - Evolution is largely a “frequently gradual” change Darwin’s Theory of Evolution by Natural Selection: - Overproduction → population produces more young than survive to reproductive age (more offspring than needed to replace parents) - Variation → variations among individuals → some better adapted → easier to survive - Natural selection → favours best suited at the time - Inherited → Best suited variants leave more offspring - Each new generation contains proportionally more individuals with favourable characteristics NATURAL SELECTION: - Natural selection → allele combinations of some individuals perpetuated at expense of other genotypes - Stabilizing selection → maintains established favourable characteristics → associated with stable environments → reduced variation (e.g. human birth weights) - Directional selection → favours genotypes at one extreme (associated with changing environments) → shift towards that genotype - Disruptive selection → rarer form of selection favouring two extremes (fluctuating environments) → gives rise to balanced polymorphism Notes on Questions: - Evolution associated with directional selection - Disruptive selection can lead to evolution is one or both of the phenotypic extremes subjected to new selection pressures SELECTION FOR HUMAN BIRTH WEIGHT: - Selection pressures operate on populations to reduce mortality - Size of baby and diameter/shape birth canal two crucial factors determining if normal delivery possible Notes on Questions: - Optimum birth weight
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