Evolution exam 1 PDF

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DETAILED summary of chapters required for exam 1. All lecture headings with examples and descriptions. Lecture notes also included...

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Evolution is NOT ○ Not a theory as used in everyday language - “speculation or unapproved assumption” ○ Not a belief - accepting that something is true in absence of scientific evidence Evolution IS ○ A scientific theory - a well substantiated explanation of some aspect of the natural world repeatedly confirmed through observation and experiment ■ Elements are testable through scientific observation/experiment ■ Details of scientific theories can & do change over time 5 main elements ○ 4 of the main elements that make up the evolutionary theory are derived from early researchers (i.e. Charles Darwin) ■ He did not know why evolution occurs bc he did not know the mechanism of genetic inheritance so he observed and recorded patterns in plants & animals ○ What did darwin notice? ■ Individuals are NOT identical (variation ■ Individuals resemble their parents (heritable) ■ Most cases, more individuals are produced than reproduced (didnt survive long or not reproductively successful) ■ Survival, & Reproductive success is NOT random (some traits are better) ○ Population vs individual ■ Evolution changes the makeup of a population, NOT an individual ● 100 fast, 100 slow. If it is better to be fast, the fast will survive and if the trait is heritable, the next gen will also be fast and the population would have evolved ○ Since darwin ■ Variation - genetic mutation is an important source of variation ■ Inheritance - DNA, genes, alleles which helps us understand “chance” events- genetic drift ■ Time - the 5th element, they knew it was old but not how old. So what exactly is evolution? ○ Some form of variation ○ Physical event that favors one variant over another (artificial or natural) ○ Increased probability of one variant being successful vs the other variant ○ Increased # of one type of variant vs the other in the next gen ○ Descent with modification (to the population) Descent with modification ○ Introduced by darwin to describe the change that occur from gen to gen within a population of organisms ○ Forms the foundation of modern evolutionary theory ○ ⅘ elements derive from descent with modification - the 5th tells us how long descent w modification has been happening Type of evolution

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Microevolution ■ Characteristic of species change over time ■ Ex: selective breeding (artificial breeding) ○ Speciation ■ # of species changes over time (one species diverges and becomes 2) ○ Macroevolution ■ New life forms derive from earlier forms (new species evolves, ancestors disappear) ■ Involves extinction ■ The “fossil record”- preserved forms of organisms no longer present ■ Transitional forms -permit connection between related species, some are fossils, some extant ○ All species are related and earth is very old Evolution - descent with modification ○ Populations are variable ○ All individuals do not survive/reproduce w same success ○ Differences in survival and or reproductive success are not random ○ The frequency of “Advantageous” trait values within populations over generations ■ The population evolves ○ It has been happening for a very long time Darwin was not first ○ There were 3 authors who wrote about natural selection before darwin ○ Alfred wallace communicated w darwin and co-presented w the darwin the first public release of their ideas in 1858 Evolution under domestication ○ Artificial selection ■ 1. Identify a desirable trait (size, color, flavor) ■ 2. Choose as breeders only those individuals with the most “ideal” values of the trait ■ 3. Repeat over many generations ■ Mutations in wild-type genes lead to desirable changes in the values of some of the traits ■ Continuous use of “mutants” as breeders reinforce the trait value as additional mutations are acquired Natural selection ○ Natural selection - the mechanism by which evolution occurs ○ Individuals within a population are different ○ At least some of the differences are heritable ○ Some individuals are better at surviving and producing than others ○ Success at survival and reproduction is not always just a matter of luck ■ Often due to the value of variable traits they inherit ■ Trait values they will also pass on to their offspring ○ Success in survival and reproduction - fitness ■ Does not mean more physically fit

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Fitness ○ “Fitness” in evolution = darwinian fitness ■ The capacity to survive and produce offspring that are themselves able to survive and reproduce ■ Darwinian fitness is not necessarily correlated with physical fitness ○ Fitness is relative ■ An individual is not either fit or not fit ■ An individual is simply more fit or less fit than other individuals ■ A trait that increases an organism's fitness relative to the fitness of other members of the species is - adaptation Testing evolution ○ Darwin's four main postulates regarding descent with modification are testable ■ The fifth, age of earth, we leave to geologists and astronomers ○ Ex: ■ Size of beaks in finches (completely natural) ■ Flower color in snapdragons (partial controlled) ○ Beak shape in finches ■ Darwin's galapagos finches - first studied by darwin ■ 13 species in 3 groups, all descended from a small group that arrived from the caribbean 2 -3 mya ■ Similar body shape, size, color ■ Tremendous variation in beak shape ■ Warbler finches ● Insects, spiders, nectar ■ Tree finches ● Use twig “tool” to access termites and insect larvae ■ Ground finches ● Seeds, ticks, leaves & fruit ■ Medium ground finch ● Found on 1 island - daphne major ● Natural setting with laboratory properties ○ Small island ○ Small pop ○ Isolated pop ○ All individuals are marked ● Ground finches are seed eaters - larger beaks eat larger seeds, small beaks eat smaller seeds ■ Drought in 1977 caused 84% of ground finches to disappear because of the decline in seed production ■ Did this lead to evolution? In the next gen the mean beak depth was 12% larger than before the drought so yes evolution occured ■ Mean beak depth of pop changed, not an individual's beak depth ■ All variation was still present following evolutionary shift ● A new beak did not emerge

● The relative frequencies of each beak depth is what changed Mean beak depth changed because the environmental factors that beak depth interacts with changed ○ Evolution of flower color ■ Jones & reithel 2001 48 flowers ■ Variability in flower color? 75% white, 25% yellow ■ SS and Ss are white, ss are yellow ■ Was variation in fitness related to variation in heritable trait? (flower color) ● White flowers attracted 2x bees as yellow ● White flowers produced more seeds per fruit than yellow ■ Reproductive success was not random ● White plants had higher fitness than yellow ■ Next gen was 77% white, 23% yellow - evolution occured Important facts regarding Selection ○ Selection acts on individuals ■ But results affect population ○ Selection acts on phenotypes ■ But evolution involves changes in allele frequencies ○ Selection does not anticipate the future ■ Always responding to current conditions ○ Selection can only act on existing trait values ■ But new trait values can evolve ○ Selection does not lead to “perfection” ■ Simply changes the frequency of certain trait values ○ Selection itself is not random ■ Although the mechanisms that make it possible, are Variability within species ○ Humans are less variable than many other species ○ Variation among individuals is the “Raw material” ○ Variation is not enough, it must be heritable ○ Protein coding (DNA sequences) define the protein “population” ○ Diploid organisms ■ 2 copies of each chromosome ■ 2 copies of each gene ■ Every protein made from 2 locations ○ Haploid organisms ■ Only 1 chromosome ■ 1 copy of each gene Coding sequence variability ○ Many protein coding sequences exist as a set of slightly different sequences within a population - alleles ■ These can produce proteins with different amino acid sequences ○ Proteins with slightly different shapes often have slightly different properties ■ This leads to different phenotypes ■

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Alleles ○ Different sequence of the same gene ○ Produce functional proteins ○ Different alleles arise when 1 or more bases in the sequence of parental DNA strand is changed (mutation) ○ Most genetic examples involve scenarios in which there are just 2 alleles (A and a) 3 kinds of variation ○ Genetic variation - variable phenotype depending on which combination of alleles are inherited from parents ■ Parents produce 2x2 = 4 alleles ■ Each offspring inherits only 2 ○ Environmental variation - differences due to exposure to different environmental conditions ■ Generally not heritable ○ Genotype-environment interaction ■ Genetically based difference in response to environmental conditions ■ Heritable Protein based genetic variation ○ Example - taste ■ Different protein receptors on cells of the tongue - products of coding regions ■ Different proteins bind to different chemicals ○ Ptc ■ Tas2r38 protein - binds ptc and delivers signal to brain ■ 2 versions of the gene for tas so the tas protein is variable ○ TAS variation ■ One variant of the TAS protein binds PTC very tightly - delivers strong signal (+) [PAV] ● Other variant does not bind it, no signal (-) [AVI] ■ Differences between them is just 3 amino acids out of 333 total ■ Humans inherit 2 copies of the TAS gene (1 from mom 1 from dad) ■ 3 genotypes possible (+/+) (+/-) (-/-) ■ 3 phenotypes possible : strong taste, moderate taste, no taste ■ This shows heritable variation but is there also selection????? ● Different versions of TAS bind chemicals found in certain green vegetables (-/-) ● Why do (-/+) (+/+) exist? ○ Vegetables contain many toxins in addition to beneficial nutrients ○ (+/-) would favor the balance and may have been the most fit genotype when humans were first here ○ (+) allele would prevent eating highly toxic plants ○ (-) allele would allow 1 to tolerate plants with just a little

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toxin but otherwise beneficial Genetic variation and evolution ○ Most variable trait value are the result of variation in the structure of proteins ○ Protein structure that convey higher “fitness” will automatically become more common in a population over time ○ Protein structures leading to decreased fitness will become less common, may even disappear over time ○ No single protein defines fitness Environmental variation ○ Most components of the environment are variable ■ Many organisms are able to adopt alternative phenotypes depending on environmental conditions - plasticity ■ Often involves some component of the environment serving to modify gene expression Environment and evolution ○ Some organisms exhibit plasticity ■ But there is no genetic variation ■ Phenotype is not heritable ○ But some types of environmentally - driven changes may be heritable ○ Epigenetic changes ■ Changes to the shape of the DNA caused by environmental factors, alter gene expression ■ These changes inherited in some cases...