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Evolution 2400 Unit 1 and 2 Notes.docx

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BIOL 2400

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Evolution*2400 Notes (Units 1 & 2) Origin of Universe Age of universe (13.7 ± 0.2 billion years) Evidence:  Expanding universe  Cosmic microwave background radiation Origin of solar system and earth (4.6 billion years) Evidence:  Radiometric dating of meteorites and moon rocks Prebiotic Chemistry Products: Amino acids, Adenine, Guanine, Cyanoacetylene, Various Sugars (ribose)  Building blocks for bigger molecules Pre-RNA to RNA Amine Bases: Adenine, Guanine, Cytosine, Uracil RNA can self-replicate  RNA bases can pair together  An RNA polymer can act as a template for replication  Self-replicating molecules can undergo the process of natural selection Why DNA versus RNA? DNA is structurally more stable and can form longer molecules compared to RNA.  RNA typically is a single stranded molecule  DNA is double-stranded Origin of Cellular Life Evidence of cellular life ~3 – 3.5 billion years ago Stromatolite-like fossils: Modern stromatolites are formed by cyanobacteria Carbon-12 and Carbon-13 ratios in preserved kerogen (organic compound) dating to 3.85 billion years suggest the kerogen was part of a living organism. Three Domains of Life Feature Bacteria Archaea Eukarya Chromosome Circular Usually Circular Linear (multiple) Structure Nucleus Absent Absent Present Plasmids Common Occasional Rare Sexual Lateral gene Lateral gene Meiosis, Reproduction transfer transfer conjugation Organelles No No Yes Unique Aspects of Eukaryote Biology:  Sexual reproduction/conjugation  Recombination  Nucleus  Complex gene regulation Hierarchical Classification Carl Linnaeus – Introduced the modern practice of taxonomy and nomenclature Before Darwin’s Theory: Observations & Ideas  Species can be classified hierarchically  Catastrophists and uniformitarianism  Pre-Darwin evolutionary observations & ideas Linnaean Classification  Linnaeus felt that species and generae were fundamental units of classification, whereas higher taxa were somewhat arbitrary  No natural mechanism to explain hierarchical classification until Darwin’s work Catastrophists & Uniformists Philosophies Phenomenon or Process Uniformitarian View Catastrophist View Theological aspects of Naturalistic (even if Always allowing for direct causes originally divine, now divine intervention always due to secondary causes) On the whole naturalistic, but allowing for occasional divine intervention Causes through geological Same causes (physical Different causes operating time laws) operative at all in early history of earth times Intensity of casual forces Always at same intensity Irregular, varying in as at present geological time Steadily decreasing with geological time Configurational causes The same at all times Different in certain former geological periods Rate of change Many gradual but some Many truly cataclysmic rather drastic changes Pre-Darwin Evolutionary Observations and Ideas Geological evidence of evolution  Fish present before reptiles, reptiles present before mammals (fossil record)  First dinosaur fossil (1824) – no dinosaurs left (extinction) Theories of evolution  John Baptist Lamark – evolution by acquired characters (1809) [not very influential]  Others published ideas that species shared common ancestors but not higher levels of classification (genera, orders,...) Three Main Components to Darwin’s Theory  Common Descent: Species share common ancestors & all life can be modeled with a phylogenetic tree with a single common ancestor  Modification: Lineages change morphologically through time  Natural Selection: Changes in the average morphological properties of a species are caused by differences in abilities to survive Current View of Common Descent Tree model of common descent is a special case of an ancestral graph  Ancestral graph allows for horizontal gene transfer and hybridization between species Ancestral graph still has property of common ancestor  Genetic units still have a single common ancestor but the common ancestor may be different between genetic units Model -> Prediction -> Support -> Theory Common descent is a model of evolutionary relationships It predicts that species are related in a tree or graph-like manner  Fits observed patterns of relationships giving it support (Linnaeus’s hierarchical classification system)  Subsequent data supports the common descent model at both morphological and genetic levels Given the strong support for common descent it is now a theory. Mendelian laws of inheritance result in common ancestors between populations that are currently reproductively isolated. If a set of species have descended from a common ancestor, how did species become different morphologically? (Natural Selection) Four premises to Darwin;s model of Natural Selection  Organisms are variable within a population  More offspring born than required to maintain population  Populations are stable in size, therefore not all the offspring survive to reproduce and certain phenotypes have a higher probability of survival than other phenotypes.  Some variation in phenotype leading to differential survival is heritable Example of Consequences of 4 Premises  Asexual reproduction  Perfect inheritance: black breeds with black and white breeds with white  Population carrying capacity  Fecundicty: both have 2 offspring per individual (overlapping generations)  Survival: white has twice the probability to survive than black Populations evolve by natural selection. Current Perspective on Darwin’s theory of Natural Selection Specific type of selection: Viability selection (survival) Example of individual selection Necessary premises are…  Organisms are variable within a population  Certain phenotypes have a higher probability of survival than other phenotypes  Some variation in phenotype leading to differential survival is heritable Viral Reassortment can lead to Highly Virulent Strains  Immune system cannot recognize distinct surface proteins  New strains can cause significant mortality (ex. Spanish flu, Asian flu, Hong Kong flu)  The H1N1 (swine flu) 2009 outbreak was a result of reassortment Evolution: The change over time in the proportions of individual organisms differing genetically in one or more traits Causes: Mutation, Random Genetic Drift, Natural Selection, Migration/Dispersal Adaptation: A heritable characteristic that enhances the survival or reproduction of organisms that have it, relative to other character states Not all Characteristics are Adaptive  Trait variation is a result of random genetic drift rather than natural selection  Trait may be correlated with another trait under selection  Trait may be an ancestral state that is not presently adaptive Example of Adaptation: Galapagos Finches  During a drought seed hardness increased on Galapagos  Birds with deeper bills survived better during drought  Birds with deeper bills can open hard seeds better than birds with smaller bills  Beak depth is heritable Deeper bills are an adaptation to open harder seeds. Fitness: The average contribution of an entity to the next generation or to succeeding generations.  Probability of survival to reproduce  Average number of offspring determined by fecundity and mating success (sexual selection) More fit do not always survive or reproduce, but on average they do more so than the less fit. Natural Selection:  Genic Selection: Selection at genetic level  Individual Selection: selection among individuals  Kin Selection: Selection among a set of closely related individuals  Group Selection: Selection among groups of individuals that need not be related  Species Selection: Persistence of a species relative to others depends on differences in characteristics of species. Example: Genic Selection Overriding Individual Selection T/t locus in mice:  tt homozygous either do not survive to reproductive age or are partially to fully sterile  there is segregation d
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