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All notes for Exam 1 - Evolutionary Biology

by: Abigail Towe

All notes for Exam 1 - Evolutionary Biology 82669 - BIOL 3350 - 001

Marketplace > Clemson University > Biological Sciences > 82669 - BIOL 3350 - 001 > All notes for Exam 1 Evolutionary Biology
Abigail Towe
GPA 3.6
Evolutionary Biology
Lisa G Rapaport

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Evolutionary Biology
Lisa G Rapaport
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This 25 page Bundle was uploaded by Abigail Towe on Wednesday September 16, 2015. The Bundle belongs to 82669 - BIOL 3350 - 001 at Clemson University taught by Lisa G Rapaport in Fall 2015. Since its upload, it has received 63 views. For similar materials see Evolutionary Biology in Biological Sciences at Clemson University.

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Date Created: 09/16/15
Evolutionary Biology Biol 3550 Week 01 Lecture Outline What is Evolution 0 evolution is the unifying theory of biology O evolutionary theory explains the diversity of life 0 in a broad sense evolution simply means change 0 a process of descent with modification from common ancestors O descent is the cumulative transmission of genetic information across generations 0 modification is the alternation in the composition of genetic information 0 common ancestry is that all of life shares a history of common ancestors 0 evolution occurs in populations 0 individuals do not evolve 0 share a common gene pool 0 evolve through changes in the proportion of different types across generations How does evolution occur 0 acts on variation 0 mutation is the ultimate source of variation 0 genetic recombination also produces variation 0 variation is sorted within a generation 0 chance results in random variation in survival and reproduction of different types 0 selection results in directed variation in survival and reproduction of different types 0 evolution occurs when the proportion of certain variants differs between generations 0 a particular type may increase or decrease due to chance 0 a particular type may increase if favored by selection adaptive O a particular type may decrease if disfavored by selection maladaptive Why is evolution a theory 0 statements based on observation or experimentation that eXplains the causes of something known or observed 0 in science a theory is not an unsupported speculation of hypothesis 0 an hypothesis is a falsifiable proposition O a fact is a hypothesis that has become so well supported by evidence that we are convinced it is true The eXistence of evolutionary change is a scientific facts 0 evolutionary theory is a group of interrelated ideas about the processes that cause evolutionary change 0 a body of hypothesis most of which are well supported with empirical evidence Evidence for Evolution 1 Evidence of change in the earth s formations A Geology 1 Relative dating 0 Fossil layers fossils are found in layers different layers contain different types of fossils O azoic layers are always deeper than zoic layers radiometric dating indicates that the earth is very old Radiometric dating using radioactive isotopes in the deep layers of Earth are used to measure time can date meteorites using this method Fossil Dead animal matter that has persisted in Earth s layers 45 46 billion years old estimation 0 stratigraphy o Stratigraphy is a branch of geology which studies rock layers strata and layering stratification It is primarily used in the study of sedimentary and layered volcanic rocks 0 Layers of sedimentary rock form strata with each layer or stratum being of a different age O superposition Radiometric dating has shown that consistently the oldest layers are deeper than younger layers Thus fossil animals and plants can be dated based upon the age of the rock found in their layer We will discuss radiometric dating in a bit 0 cross cutting relationships 0 Rocks that intrude into seams in other rocks or as dikes are always younger than their host rocks Sedimentary rocks sandstone limestone form original layers Igneous rocks such as lava or basalt run into cracks and crevices in layered sedimentary rocks 0 Fossils can only be fossilized in sedimentary rock Need pressure and water 0 faunal succession O The oldest fossil forms often contain more primitive features and more recent fossils contain more derived features characteristic of living forms This example shows a faunal succession of trilobites 0 Location of fossils allows reconstruction of phylogeny and time since divergence from common ancestors 2 Absolute dating radiometric methods 0 Potassium Argon O Carbon 14 0 Geologic Time Scale Order B Phylogenies reconstruct evolutionary history 1 SinosauropteryX and the evolution of feathers httpwwwvoutubecomwatchvhPLngX115Y feather not always for ying camo aug for example httpswwwvoutubecon watchv12C 3PiNGok 2 Clado grams C Early hypotheses to eXplain changes on the Earth 1 Catastrophism Cuvier 17691832 series of floods and successive sedimentation accounts for different layers or strata each successive fossil layer represents separate creations by God such catastrophes have not been observed in historic times 2 Uniformitarianism Hutton 1788 Lyell 1830 geological processes now are same as in the past geological processes are gradual implies that the earth is very old Thus processes operating today can account by extrapolation over long time periods for the evolution of the earth and of life 11 Evidence from the Fossil Record A The Fact of Extinction 1 CuVier 1812 2 P w Description of fossil extinct Irish Elk Extinct species are relatives of living species found today B The Law of Succession 1 Close relationship between fossil and extant species from the same geographic area 2 Close relationship between fossil forms in adjacent rock strata C Transitional forms 1Contain characteristics of ancestors and some of the descendants Novel descendants Ancestral ancestors Whales Tiktaalik large freshwater sh has scales and n of sh but had at and rotating neck of land animal had beginning of bone structure of 4 limb animals today lower arms and wrists transitional animal go on to spawn reptiles and eventually humans III Evidence of common ancestry A Homology suggests common ancestry homology provides strong evidence 0 not just looking at fossils but developmental parts 0 examples embryos of fish reptile bird and humans all have gill slits in all embryos indicating a fish is common ancestor l Analogous have common function but not a common embryonic origin 0 example bat wings to insectbird wings they are analogous because they are similar but don t have a common origin 2 Homologous structures have a common embryonic origin but may or may not have a common function through looking at embryonic dev you can see the bone structure between batsbirdsinsects are very similar 3 Convergent natural selection leads to analogous body forms example sharks and whales same streamline shape but is not from common evolution 3 Homologies that are not analogies provide the strongest support for common ancestry O homologous bones in vertebrate forelimbs O humans horse birds bats seals turtles with the similar forelimbs 4 Genetic homology from genetic code that is nearly universal across all life on earth few exceptions O for example codons that code for proteins B Evolutionary Change can create new species 1 artificial selection 0 for example people have known for a long time that artifical selection can create new breeds of animals or specific kinds dogs came from domesticated wolves 2 natural selection more randomized crown group descendants still living Evolutionary Biology Biol 3550 Week 03 Lecture Outline Historv of Evolutionarv Thoug Early ideas about species A Plato s notion of the type 1 Ideal form existence of an ideal form eidos o visible world was a manifestation of that form with imperfections 2 Fixity ideal form does not change fixity of species B Aristotle 1 Scala naturae Scala Naturae or the Great Chain of Being 2 Implications of Aristotle s scale of life o progression from most complex to least complex 0 every organism is ordered in relation to humans which are at the apex o organisms are unchanging since they are created in perfect form 0 change would imply imperfection in the original creation 0 impossible for new forms to have arisen since creation or for existing forms to have gone extinct C The Renaissance in Europe European thought during the Renaissance Stasis o the earth was full and as it should be c the result of God s grand design L D The age of expansionism amp the scientific revolution The Scientific Revolution 1 Why did this period usher in different thinking about species and our place in nature 0 Expansionism discovery and exploration of new areas I examples South and North American and Central amp Southern Africa 0 so people started to see unimaginable things hard to describe sights and knowledge they tried describing new creatures o Advances in Science and Technology 0 Astronomers I Copernicus determined earth revolved around Sun huge change because people thought earth was center of universe I Galileo and Kepler later supported Copernicus theory Galileo Italian wasn t allotted for his discoveries o Mathematicians I Descartes French man developed geometry and studied some anatomy to learn functions of body usually people thought of spirits for explanations I Newton 0 Printing Press helped to spread new information so much faster than before I Gutenberg 2 Carolus Linnaeus published Systema Naturae in 1735 o Developed the modern classification scheme that we still use today 0 a strict believer in the fixity of forms deal form does not change fixity of species ll Discovering a world in flux A Comparative biology 1 George Cuvier o lived in 18th century Renaissance o unity of structure 0 each species had its own harmony of parts 0 species are discrete entities o he thought that perhaps groups of species that look similar to each other could have common harmonies 0 common harmonies extended to extinct species I didn t really look at a matter of being related to each other just similar 0 first scientists to acknowledge extinct species 0 2 Why was his examination of extinct forms important to his thinking B Organic Mutability 1 Evidence from artificial selection evidence that plants and animals were not constant in form 0 species could change through artificial selection 0 tremendous amount of variation could be harbored in a single stock 2 Gilbert White 1780 different breeds of pigeons traced back to rock doves o looked at all species and how they functioned in their environment 0 he made ecological link to certain birds to certain environments I After doing this detailed study he hypothesized that the domestic pigeon came from wild blue bird some sort lmplying ancestor o many diverse forms can arise from a single C Principles of geology calculated extinction rates from fossil record 0 extinction rates were relatively constant from layer to layer 0 He asked himself why aren t all the species found today not represented in oldest strata 0 periods of major extinctions correlated with periods of environmental change 0 process of selection was obviously eliminating species that were unfit for new environmental conditions D Lamarck 1 Theory of inheritance of acquired characteristics 2 In what respects was Lamarck s theory innovative and correct What important link did Lyell make between extinction and the environment Inheritance of acquired characteristics I Jean Baptiste de Lamarck 0 use and disuse alter body form during an individual s lifetime 0 organisms change form in response to changing environment E Species selection versus Individual Selection 1 selection among species a more fit specie survived less fit species went extinct 2 evolution was differential sorting of chance variations among species 3 One more F Theory of inheritance of acquired characteristics G In what respects was Lamarck s theory innovative and correct F Species selection III Charles Darwin A Early life and voyage on the Beagle o upperclass family 0 studied at University of Edinburgh medicine and Cambridge theology o Naturalist on long term British navy expedition of HMS Beagle sma ship 1831 1836 0 this is where he did most of his observations to develop his theory 0 Route New England South America around Cape Horn Galapagos touches Australia Indonesia Cape of Good Hope of Africa and then back to South America then back home to New England o published On the Origin of Species by Means of Natural Selection in 1859 0 Notice he spent a lot of time examining other collections and doing experiments before publishing this book B Observations from the Galapagos o mockingbirds from different islands looked like different species 0 same was true for tortoises and finches o bills appeared to fit remarkably well with available foods 1 tortoises 2 finches beak sizes change 3 Linking variation to the environment 0 Darwin noticed that island birds changed in character when other competitors lived on the same island o The more species the more specialized their beaks o Fewer species more generalized beak shapes C Postulates of Natural Selection 1 Hypothesized that individuals within species are variable 2 Certain of these variants are passed on the offspring sometimes traits are passed down but not always 3 In every generation more offspring are produced than can survive o Individuals within certain species can reproduce exponentially but the environmental support for that individual is limited so some will survive but not all 4 Differential survival and reproduction struggle for existence 0 only those individuals with favorable variations live to reproduce and contribute offspring to the next generation 0 these individuals are NATURALLY SELECTED 0 hence the mechanism of evolutionary change D Evidence for Natural Selection Fur color in Beach mice 0 the Grants are studying the effect on DanNin s medium ground finch of 19761978 drought on Daphne Major of the Galapagos Islands 0 During this study there are years where there are good rains but some years of serious droughts 0 Tracking them taking beak size etc to study how the finches change with the environmental changes E Alfred Russell Wallace another naturalist living at the same time as Charles Darwin 0 Came from a middle class family one of 9 kids He had to quit school at age 14 and went to work as carpenter with his brother for a while Later he went to explore and collect forms of life 1 Wallace s proposed theory of evolutionary change through natural selection 0 sent his paper to Darwin in June of 1858 o Lyell read paper by Wallace and paper by Darwin were both read at annual meeting of Linnaean Society in London later that year DanNin s was read first so it was published first Lyell and DanNin claimed that they had Wallace s permission to read and publish but Wallace said that he never gave permission 0 Darwin published The Origin of Species in November 1859 2 Evidence Observations c He did his observations in the Amazon River Basin 4 years and then Malaysian archipelago 8 years c He became a collector by trade which caused him to notice variation of traits within species 80 he noticed all of the variation as he collected and comparedquestionedbegin to study and take notes on them 3 Biogeography the Wallace Line 0 Separation of Asian and Australian flora and fauna in as little as 20 miles F DanNin and Wallace s Great Idea 1 Selection occurs among individuals not species a the traits are either favored or disfavored 2 change is gradual a selection works on small differences among individuals Role of ecological change 4 role of sexual selection 00 Lamarck s view 0 species arise individually o complexity increases through time DanNin s view 0 species arise through common ancestry o complexity may increase through time G Evidence that Darwin Presented in On the Origin of Species artificial selection selective breeding geographical distribution of species and traits geography embryology anatomy vestigial organs fossils He wasn t comfortable publishing until learning massive amounts of information W 1 Vestigial structures humans have vestigial structures appendix coccyx goose bumps wisdom teeth amp pica semiluniminaris pink part in corner of eye 2 Fossils 0 Darwin knew of fossils studied them in detail If evolution had taken place the fossil evidence should show intermediate species traits partway between two modern species further back in time o hypothesized the existence of intermediate prehuman fossils 3 Not aware of plate tectonics or genetics 0 the earth s landmass began as a huge supercontinent Pangaea 0 About 245 million years ago the plates that form the earth s crust began to move apart which caused the single landmass to break apart H 1 No goal 2 Not necessarily progressive lV Natural Selection in Action A What is Selection 0 A mechanism of evolution 0 Genetic Drift is another example 0 The process of differential survival and reproduction by those individuals in a population that are better higher survival and reproduction or more poorly lower survival and reproduction adapted to their environment selection acts on phenotypes and indirectly on the genes that produce them Thereby causing a change in gene frequencies over time or promote stability in gene frequencies so it doesn t necessarily mean change How is natural selection measured 1 Stabilizing selection Selection agei t bath extremes Peple lien after selection Dr iginel popwiatien Mean value of the trait is highest More narrow distribution that centers on the mean 2 Directional selection ll m 391 1 5 r r EA I r 39 I E 5quot 39l Directional selection of beak depth in medium ground finches The mean beak size shifted to thicker beaks after drought because that s the most successful beak for finding food 3 Disruptive selection ENEmm Egmt 5 MLquot Ilft it It ling El aim 39 nighquot i39i ESE ail n L V 39 rur a a 9 y untta 39 m w E ah h h Hf Individuals with mean value is selected against Extremes of trait are selectedfavored could eventually lead to speciation B The Case of Fur Color Evolution in Beach Mice beach mice from Florida come in a variety of colors light to dark Scientists have categorized them in subspecies according to color Facts C old field mice beach mice Location Southeast USA Habitat sand burrows in dunes or old fields Home range 1000 mquot2 Breeding monogamous pairbonding Litters of 28 pups every 30 days Lifespan 912 months Eat vegetation and bugs Predators owl fox weasels bobcats snakes I Prey on mice by sight and sound Visual predators o light furred species live near white sandy beaches o darker furred species live near darker beaches 0 C O C O C 0 Question o Assuming that ancestral populations of beach mouse had dark brown fur what could have happened to explain the occurrence of lightcolored coastal subspecies o What mutations What kind of biochemical pathways have been affected Hypothesis light furred mice survived longer than darker ones on beaches thus they reproduced more and caused a shift in fur color 1 Ecology of fur color 2 Cell biology of fur color 0 hair color are affected by two pigments I eumelanin darker colors 0 When is eumelanin produced o A transmembrane protein the melanocortin 1receptor MC1 R is stimulated by a hormone called the alphamelanocyte stimulating hormone alphamsh to produce lots of eumelanin Can only bind to alpha msh I pheomelanin lighter colors I 3 Genetics of fur color 0 The mc1r gene is located chromosome 16 in mammals o A single nucleotide substitution can lead to a change in the MC1 R protein chain 0 A single mutation of cytosine to thymine changes the amino acid in position 367 from an Arginine to a cysteine o The mc1r gene has two alleles R for arginine and C for cysteine Arginine codes for functional mc1 r protein but cysteine codes for nonfunctional mc1 r protein so it prevents binding and changes the pigment pathway 4 Population genetics of fur color 0 there are 3 possible genotypes associated with the mc1 r gene 0 RR arginine arginine indicates that both copies of chromosome 16 has an arginine amino acid at position 67 of the mc1 r gene Eumelanin 0 CC gt Cysteine cysteine indicates that both copies of chromosome 16 has a cysteine amino at position 367 of the mc1 r gene Eumelanin 0 RC has both o Is there a relationship between fur color of each mouse individuals and the allele combinations genotypes they possess 5 Simulation Evolutionary Biology Biol 3550 Week 4 Lecture Outline Review 0 selection does NOT have a goal 0 the environment favors certain traits I example finches in drought a thicker beak is favored 0 Evolution is not intrinsically progressive 0 many simple forms have stayed virtually unchanged for hundreds of millions of years 0 some complex forms have become extinct 0 some complex forms have become simpler O increasingly diversity of life on Earth I Ancestral Free living mite need microscope to see them 0 parasitic skin mite O free living dust mite Merger of Darwin amp Mendel I Dilemmas amp Critiques of Darwin s Theory A Stability and effectiveness of change 1 Natural selection is too limited 2 Small differences are not large enough 3 W Castle s experiments on hooded rats 9 arti cial selection on racing stripe width in hooded rats b recombination through backcrossing to control line wild type allowed for new phenotype with wider stripe to evolve c multiple genes were responsible for variation in stripe width d continuous range of widths e recombinations of multiple genes extends the limits of selection f ends up increasing width over time i after getting a really wide stripe he then bred them with the narrower stripe B Maintenance of variation 1 Why was concept of blending inheritance a problem a Blending Inheritance Fleeming J enkin 1867 does not allow for variation among individuals to be maintained 2 Why was concept of that most variation was the result of environmental variation a problem a also during this time it was thought that most variation was thought to be environmentally induced i negates the idea that Darwin had of passing variation from parenting to offspring How can it be parent to offspring if it s affected by environment 3 Poor survival of mutants a mutants were thought to arise so infrequently that their establishment and evolution into new species was impossible Continuous variation results from the inheritance of discrete genes 0 Discrete traits like pea coat color which are determined by a single gene are actually rare 0 most traits are determined by the effects of multiple genes 0 these polygenic traits show continuous variation 4 Polygenic traits a Corolla length in tobacco b depending on number of genes different numbers of phenotypes were predicted c one gene 3 phenotypes d two genes 5 phenotypes e if Mendelian model works the parental phenotypes should reappear through selective breeding f east selectively bred for both short and long corolla lengths g by generation 5 the length was nearly same as parents C Natural selection could not explain speciation l Speciation via allopatric adaptive divergence a relationship of divergence to speciation i no mechanisms that promote speciation were known such as reproductive isolation ii adaptive divergence can result in reproductive isolation between species iii reproductive isolation can evolve as a by product of adaptive divergence in geographic isolation 2 Sympatric speciation via assortative mating Benthic and limnetic threespine sticklebacks O benthic mainly eats invertebrates large body and few short gill rakers O Limnetic primary eats plankton small body and many long gill rakers lab experiments show that there is size assorted mating large mates with large D Observed punctuational change over time 1 Rapid evolutionary change has been observed a short period of rapid change followed by long periods of stasis b natural selection should result in gradual continual change c we now know natural selection can result in very rapid evolutionary change as well as long periods of stasis i this is because natural selection changes in populations where the environment changes ii changes in the environment drives the changes 2 Example of intense natural selection and subsequent rapid evolution a micro examples antibiotic resistances antiviral resistance b macro example escape ability in Trinidadian guppies i guppies in streams 1 moved them to streams in high predation and low 2 within 20 years guppies from high predation populations had much higher survival rate when placed in enclosure with a predator 3 F2 generation from high predation population raised in predator free enclosures also had greater escape ability when placed with a predator 4 escape ability is a rapidly acquired heritable trait 11 Contributions of Mendel A Mechanism of heritability mendel solved the heritability problem 1 Discrete traits 1 particular inheritance of discrete traits 2 Independent assortment amp segregation 1 independent assortment and segregation of alleles produce variation 1 not all variation is dependent solely on mutation B Problems Mendel did not solve 1 Inheritance of continuous traits Mendel s laws were based on discrete variation b much variation in natural populations is continuous c thought that environment not heredity controlled eXpression of continuous variation d continuous traits can have really high heritability values 2 Example beak depth in ground finches III The Modern Synthesis A Population genetics a developed in the 1930s early 1950s b shows that mutation is not an alternative to natural selection c actually creates lots of variability d mutation is the raw material on which natural selection and other forces of evolution actually act B Genetics amp Natural Selection combined a evolution results from small gneetic changes that are acted upon by natural selection b process operating within species account for the major long term features of evolution i microevolutionary forces are responsible for macroevolutionary change origin of species ii anagenesis leads to cladogenesis 1 both speciation C Restating Darwin s Postulates in genetic terms 1 Individuals within species are variable 0 due to mutation creating new alleles O recombination shuf ing existing alleles into new combinations 2 certain of these variants are passed on to offspring alleles are passed on unchanged from parents to offspring 3in every generartion more offpsinrg are produced than can survive 4 differences exist in survival and reproductive rates among individuals 0 individuals who contribute more offspring to the next generation are those with alleles or allelic combinations that produce traits that are best adapted for the particular environmental features encountered 0 therefore those alleles that favor survivability and reproduction will increase in frequency in the next generation D Evolution is a genetic process a evolutionary change is the change in allele frequencies from one generation to the next in a biological population b evolutionary change occurs by means of natural selection when alleles associated with higher fitness increase in frequency from one generation to the next IV Stuart et al 2014 A Elements of a scientific paper B Discussion of results September 15 2015 Variation among Individuals Producing Genetic Variation 0 Variation among individuals 0 through genetic environmental and genebyenvironment interaction I Genetic Mutations A How do new allele arise 2 general mechanisms whereby new alleles are created Mutations occur through 1 mistakes that occur during the DNA replication process caused by the failure of one of the DNA repair mechanisms 3 ultimate source of genetic variability B Point Mutations 1 Single basepair A C T G substitutions 0 not repaired by proofreading or mismatch repair 0 after synthesis a new allele is created Two general types of point mutations Transitions and transversions O Transitions are interchanges of tworing purines A H G or of onering pyrimidines C H T they therefore involve bases of similar shape 0 purine to purine o pyrimidine to pyrimidine O Transversions are interchanges of purine for pyrimidine bases which therefore involve exchange of onering and tworing structures 0 purine to pyrimidine Which are more frequent Why 9 Although there are twice as many possible transversions because of the molecular mechanisms by which they are generated transition mutations are generated at higher frequency than transversions As well transitions are less likely to result in amino acid substitutions due to Wobblequot and are therefore more likely to persist as quotsilent substitutionsquot in populations as single nucleotide polymorphisms SNPs 2 Insertions amp deletions o Dinucleotide repeats are formed by slippage replication 0 slippage replication a form of mutation that leads to either a tri nucleotide or dinuoleotide expansion or contraction during DNA replication A slippage event normally occurs when a sequence of repetitive nucleotides tandem repeats are found at the site of replication Tandem repeats are unstable regions of the genome where frequent insertions and deletions of nucleotides can take place resulting in genome rearrangements 0 basis of satellite alleles o more common in noncoding regions 0 What are they and how do they occur 0 O rearrangement because tandem repeats are unstable regions Where do they commonly occur during DNA replication occurs within a repetitive nucleotide C Consequences of point mutations 1 Silent substitutions o How do they occur and what is the result 0 single nucleotide changes that do not change the amino acid encoded by the mRNA 0 usually involved changes that will affect the third position of mRNA codons 0 about 70 of point mutations are silent 0 results in NEUTRAL mutations o synonymous same amino acid as before 0 We have this because degeneracy of the code yields many opportunities for silent substitutions 0 when it s the third position that has been changed it s usually the synonymous substitution but sometimes it does change missense substitution 2 Missense substitutions How do they occur and what is the result 0 single nucleotide changes that DO change the amino acid that will be coded o lst or 2nd position alteration 0 create what are called null alleles such mutations are usually recessive and deleterious or lethal o occasionally such mutations create beneficial alleles o which opens new possibility of new adaptation for individual 0 nonsynonymous substitutions because the functioning of the protein is NOT the same 0 example Sicklecell anemia o the hemoglobin protein has a single base pair substitution in the protein that changes the glutamic acid to valine this creates a protein with an impaired function 0 this mutation is lethal in homozygous condition 0 heterozygotes are favored in regions with malaria 3 Nonsense substitutions How do they occur and what is the result 0 changes in DNA that results in insertion of a premature STOP codon into the mRNA ATT UAA ATC UAG UGA early stop signal in mRNA halts translation protein is nonfunction 4 Frameshift mutations o How do they occur and what is the result addition or deletion of one or a few nucleotides causes a shift in reading frame of mRNA that will be transcribed all codons downstream of the indel will be changed 0000 results in production of a nonfunctional protein Chart from class Examples of loss of function mutations Point mutations No mutation Silent Nonsense Missense censervative henconservative DNA level mRNA reves AAG AAA UAG AGG ACG rxotem fever Lys Lys STOP Arg Thr D Mutation Rates 1 Spontaneous mutations How often do they occur 0 mutations occur by change at low frequency 0 about 10quot9 or 1 per billion nucleotides replicated in mammals o spontaneous mutation rate varies among genes and among species 0 many alterations to DNA are repaired and do not become persistent mutations Examples 0 Drosophila fruit fly 0 wild type for eyes red o spontaneous mutation leads to brown eyes I occurs 3X10quot5 times per replication I point mutation on chromosome 2 0 changes from enzyme A scarlet pigment to enzyme B brown 0 but when both enzyme A and B are produced then you have a dark red eye 2 Recurrent mutations 0 mutations that arise repeatedly o albinism in mice is a recurrent mutation 0 wild type to albino 10quot5 gamete generation 3 Induced mutations o Mutagens are substances that increase the mutation rate above the spontaneous rate 0 ultraviolet light 0 ionizing radiation 0 pesticides and industrial chemicals 0 quotcancer causing agents that induce mutations E Mutation is a Random Event 1 Mutation RATES are affected by environment 0 mutations are random events but the rate can be affected by environment 0 the kind of mutation that arises is not directed by environment it s a chance event 0 whether or not the mutation persists depends on the environment 2 Mutation is NOT DIRECTED with respect to the environment 0 exposure to mutagens will increase overall mutational rate but not determine which particular genes will be affected Ill Chromosomal Mutations Large Effects A How do mutations cause changes in genomes 1 Karyotypic mutations o genome duplication polyploidy o Entire sets of chromosomes is duplicated 0 can occur by two different mechanisms sources 0 Allopolyploidy the duplicate sets of chromosomes come from two distinct sources 0 creates hybrid o Autopolyploidy the duplicate sets of chromosomes come from the same source 0 creats triploid 0 Both can result in the nearly instantaneous origin of new species 2 Chromosomal mutations 0 Gene Duplications o unequal crossing over 0 a piece of a chromosome is duplicated during crossing over can involve one or multiple genes 0 caused by replication errors something gets copied twice 0 How do they occur 1 homologous don t pair properly so after crossing over one chromosome has a deletion and the other has a duplication 2 occurs rather easily if DNA contains many tandemly repeated nucleotides or genes microsatellites 3 often the new gene is not functional pseudogene 4 sometimes create new genes that may then diverge in function 0 Why are these errors important 0 thought to be important mechanism in the evolution of multigene families I Example Hemoglobin gene family o paralogous genes and pseudogenes r The major Hemoglobin chains r Different genes for different globins alpha and beta chains r the gene for the alpha chain is derived from duplication of the gene for beta chain recent duplication created the second alpha chain r different hemoglobin proteins are produced at different developmental stages r different globin proteins are produced in different tissues 0 cytoglobin myoglobin etc IV Importance of mutation A Mutation as a evolutionary force 1 mutagenic change in populations a mutation is NOT a STRONG evolutionary force i probability of survival of a rare mutant is low ii survival of a rare mutant is higher if recurrent mutation iii survival probability of a rare mutant is higher if 1 mutant is favor by natural selection and 2 population is rapidly increasing in size 2 importance of mutation as a evolutionary force a mutation creates variation i the only source of unique alleles ii rate of accumulation of mutation variation can be fairly high for polygenic traits b mutation provides the variation needed by other forces of evolution i neutral alleles are acted upon by genetic drift ii advantageous and disadvantageous alleles are acted upon by natural selection 0


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