Bio 200 Week 3 Notes
Bio 200 Week 3 Notes BIO200
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This 11 page Class Notes was uploaded by Nicole on Friday September 18, 2015. The Class Notes belongs to BIO200 at University at Buffalo taught by Dr. Lindqvist in Summer 2015. Since its upload, it has received 67 views. For similar materials see Evolutionary Biology in Biology at University at Buffalo.
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Date Created: 09/18/15
September 14 2015 Lecture 4 Darwin s Evidence Hypothesis for natural selection Evidence for Darwin s hypothesis from his lifetime Modern evidence Implications of Darwin s hypothesis Evidence to support the implications Darwin s Hypothesis Three Parts There must be variation in population Variation must lead to differences among individuals in lifetime reproductive success Variation must be transmitted to the next generation Modern Five Parts Individuals vary Populations tend to overbreed relative to available resources leading to a struggle fro survival Better variations have better survival Survivors will reproduce amp nonsurvivors won t not always necessary criteria Traits leading to better survival amp reproduction must be heritable Do Individuals vary Yes Do populations tend to overbreed Yes Oak trees put out many more seeds that can possibly survive Somewhere between 00101 of seedlings are expected to survive One oak tree will release over one thousand acorns in its lifetime Do better variations for a particular environment have higher survival rates Darwin could not tell because he could not determine which variations were better Today we are much more able to test and confirm this fact as there is much more data to support it Rosemary and Peter Grant worked on Daphne Major Island in Galapagos Two of Darwin s finches live on this islandlarge and medium ground finch Variation in head amp beak size in medium ground finches Survival of these birds is based on seed availability 1977Severe La Nina Extreme drought extreme population decline from 1400 finches to 200 finches in just one year Soft seeds quickly eaten leaving only hard seeds remaining Birds with longer and deeper beaks outsurvived those with smaller beaks 1984 El Nino very wet year Abundance of small seeds can fall out of large beaks Smaller beaked birds survived better than those with large beaks Solidifies theory that better variations have better survival rates Do survivors have more offspring and pass on their selected traits to the next generation Darwin doesn t know We know that the 1977 survivors had bigger beaks but if these larger beaks were acquired the birds would not pass this trait on to their offspring amp would not shape evolution across generations We must look at the offspring to see if traits were inherited Grants plotted beak size of parents by the beak size of offspring amp found very strong correlation strongly suggests that traits are heritable Evolution actually changed the average beak size across generations causing more birds to have large beaks Concludes that traits leading to better survival and reproduction must be heritable Why isn t everyone satisfied Implications Involved in accepting this theory Earth must be old enough for evolution to have occurred Fossils should show evidence of change through time Older rock strata should have fewer fossils of modern species than younger rock strata Fossils of intermediate forms must be found Is Earth Old enough Hutton amp Lyell both believed so Depth of canyons amp thickness of rock strata both indicate very long amp gradual natural process We can now date the oldest found rocks to be 46 billion years old Found oldest life to be about 38 billion years old Earth is old enough Do fossils show that species are mutable Cuvier showed that extinction occurred and that recent species were no longer extant Darwin s fossils MegatheriumGiant sloths 11m tall amp weighed up to 6000 lbs Toxodon capybara like species 15m tall amp weighted up to 15 tons GlyptodonGiant armadillos 15m tall weighed as much as average sedan Fossils were closely related to animals alive at the time but were not the same spec1es Do younger rocks strata have more modern fossils than older rock strata Lyell has data on mollusks 1854 Era MYA Known Species Still Alive Recent Pliocene 3 226 96 Older Pliocene 6 569 42 Miocene 25 1021 17 Eocene 50 1238 3 Data helped Darwin with 3rd implication Are there fossils of intermediate forms 3 years before his death Archaeopteryx fossils were found Has traits of both birds and reptilesintermediate form Provides solid evidence of transitional forms Transitional Forms Whales Landdwelling 4hoofed mammals transition to whale Tiktaalik Found 2006 in Canada Transitional form between fish amp amphibian Gills and scales like fish neck like amphibian Had shoulder forearm amp wrist like modern amphibian but end was lobed fin Horses All modern horses zebras donkeys members of Equidae Family Horses used to be incredibly diverse First horses the size of mediumsized dog Fed on vegetation amp lived in woody areas Transitions in Anatomy amp Behavior mark adaptation in Equidae Hyracotherium Modern Horse Size Small short legged Large long legged Feet Broad foot Narrow foot Toes 4 front 3 back One Teeth Small amp simply shaped Large with ridges Habitat Forest Grassland Feeding Browsing Grazing Changes may be due to altered climate Darwin s Evidence 1St evidence of plant hormones Explanations of ower design Expression of emotion in animals Power of movement in plants Evolution of insectivorous plants Human evolution Barnacle evolution How coral reefs were formed Mechanism of Evolution Thomas Hint Morgan 48661945 Drosophila genetics Mechanical basis of heredity chromosomes Theodosius Dobzhansky 19001975 Genetics amp the Origin of Speciesquot Nothing in Biology makes Sense Except in the light of Evolutionquot Modern Evolutionary Synthesis Evolution as changes in allele frequenciesquot Serwall Wright 18891988 Ronald Fisher 18901962 IBS Haldane 18921964 Founders of populations genetics Mathematical models of evolution Statistical genetics September 16 2015 Lecture 5 Mendel amp Basic Genetics Gregor Mendel amp collapse of blending model Mendel s basic process Mon Family Resemblance Farmers have used breeding techniques to enhance crop and livestock traits for centuries Most people believed that traits were blended from parents to create intermediate form in offspringNot true If all traits are blended throughout time eventually all species will look the same Gregor Mendel 18221884 Educated in a monastery Plant hybridizationfocused on how traits are passed down through generations Used pea plantsthey regenerated quickly amp were easy to manage Needed true breeding plants When the plants reproduce all offspring look like the parents Mendel looked at ower color Ensured that when purple owered plants together they produced purple owered plants When true breeding plants were produced Mendel would cross true breeding plants of 2 different truebreeding traits Ex white owered plants with purple owered plants Observed hybrid offspringcounted how many of each plant had different color owersthis quantification of results was very important Mathematical analysis allowed Mendel to observed that traits appeared in predictable ratios Monohybrid Cross P generationParent generation made of truebreeding plants one purple one white Cross fertilize F1Generation all purple Selfcrossfertilization of same plant pollen came from F2Generationshowed 31 ratio in nearly every trait 3 purple 1 white F3Generation13 purple bred true 23 purple had 31 ratio in offspring and the white owers always bred true Shows that blending inheritance does not happen Unexpressed traits can be latent and reappear in later generations white owers Mendel s FiveElement Model Parents transmit information about traits to their offspring Each individual receives two copies of each factor to encode each trait Not all factors are the same and different combinations lead to different traits Two factors do not blend Presence of a factor does not guarantee it will be expressed it can be latent Genotype Alleles found in individuals Homozygote dominant has different genotype that heterozygote dominant AA differs from Aa even if both owers are purple Genotype ratio 121 Phenotypes AAAa Physical characteristics of organisms Phenotype ration 31 Mendel s 1st Law of HeredityPrinciple of Segregation Two parental alleles segregate during gamete formation to be rejoined at random during fertilization Punnett Square Aa with Aaboth heterozygotes A a A AA Aa a Aa aa 31 ratio Dihybrid Crosses Parental Generation RRYY rryy F1 RrYy Dihybrid Crosses lead to 9331 Ratios in phenotypes Source httpCnxorgresourcesceb880bf9a58402dc053bb94ff94ec158ffc2a3 aFigure 12 03 02png Mendel s 2nd Law of HeredityPrinciple of Independent Assortment In a Dihybrid cross the alleles of each gene assort independently As far as Mendel was Aware Factors assort independentlyGene linkage Each trait is controlled by a single factor Factors do not interact Each factor controls only one trait Factors only have two alternative outcomes Factors are unaffected by the environment they are expressed in quotMendel was wrong on all of these ideas Genes are Sometimes Linked Certain alleles are almost always expressed together Linked genes are on the same chromosomes and do not assort independently Polygenic Inheritance Mendel s traits were all two state cases ex purple or white smooth or wrinkled This is not true with many other factors including plant height Polygenetic inheritancetraits can be controlled by multiple factors Some genes add height some reduce itmust add all in uences together to determine height of plants EpistasisLab coat color determined by 2 genes that interact Without knowing gene type it is impossible to know dog color Sickle cell anemia Multiple effect of one genedecreased ability to transport oxygen but decreases susceptibility to malaria Dominance is Not Always Complete Incomplete dominance Parental phenotypes blend in the heterozygote Blending ends with the heterozygote Codominanceheterozygotes show both parental phenotypes unblended Dominance is not always complete codominance Environmental Differences Effect on Factor Expression Siamese cats melanin in Siamese cats is due to temperature near core temperature is too high to allow expression of melaninproducing enzyme September 18 2015 Lecture 6 What Mendel Didn t Know Mendel 18221884 1866no knowledge of chromosomes genes or DNA Chromosomes Discovered in 1879 did not believe that they were related to genetics Chromosomes come in pairs and are linked to inheritance Each person contains one set from mother and one set from father Every organism has chromosomes but the number each species has varies greatly Humans have 46 chromosomes 23 from mom 23 from dad Karyotypes Map of a set of chromosomes Mostly chromosomes are unreplicated and very hard to see Homologous pairs are shown on karyotype Terminology ChromatidsWhen chromosomes condense amp become visible but before they replicate Sister ChromatidsThe two identical chromatid copies formed during replication CentromerePart of the chromosome that links sister chromatids ChromosomePair of sister chromatids form the chromosome Homologous PairSame chromosome type from mom and dad Mitosis Interphase DNA is diffused and hard to see Phase where DNA is replicated Only phase of cell cycle where DNA is accessible to proteins involved in replication Prophase Mitosis begins Chromatin becomes more compact amp becomes visible Now consist of identical sister chromatids Mitotic spindle formsstructure that will pull the cell apart Prometaphase Nuclear envelope breaks down Kinetochore microtubules which are connected to the poles attach to the chromosomes Metaphase Chromosomes line up at midline of cellEquatorial position Chromosomes are condensed and highly quarreled Anaphase Sister chromatids are pulled apart to opposite ends of the cell Telophase Last phase of mitosis Chromosomes are fully separated Cell cleaves in half to form two daughter cells Daughter cells have same number of chromosomes as parent cellidentical copies Meiosis Only occurs in gonadsleads to sperm amp eggs in humans Following interphase chromosomes begin to condense and a meiotic spindle forms Homologous pairs join in center of cell Each chromosome will end up at each end of the cell Cell divides to form 2 daughter cells Daughter cells are genetically distinct amp have only half as many chromosomes as parent cell when gametes join there will be the right number of chromosomes Ploidynumber of copies of chromosomes A cell with one copy is a Haploid 1NGametes Cell with 2 copies is a Diploid 2N More than two copies is a polyploidy xN Mitosis 2N94N92N Meiosis 2N94N92N91N Sex Chromosomes Crossing Over Occurs in the beginning of meiosis when homologous pairs join Enzymes break amp rejoin chromatids on homologous chromosomesDNA from non sister chromatids can be exchanged Now chromosomes from dad may have DNA from mom s chromosome on it Chromosomes may have many or very few crossovers Recombination Now genetic material from parents is mixedleads to much higher variation among offspring Gene Linkage When genes are unlinked the F1 generation can produce gamete combinations When traits are linked A will not appear with b and B will not appear with a Distance between genes on chromosomes has a lot to do with whether or not they will be linked Genes close together on chromosome are tightly linked while genes further apart are loosely linked as they can be easily separated during recombination Wilhelm Iohannsen 1909 Coins the term gene Thomas Hunt Morgan 1910 Genes rest on chromosomes George Beadle and Edward Tatum 1941 One gene codes for one enzyme Oswald Avery Maclyn McCarty Colin MacLeod 1944 Genes are made of DNA Rosalind Franklin 1952 Used XRays to determine double helix structure of DNA Watson amp Crick used her photograph to publish findings on DNA s structure DNA Double helixtwo strands of genetic material Backbone made up of repeating sugar and phosphate units Hbonds hold nucleotides togetherspecifically pair certain nucleotides together Four nucleotides Adenine A Thymine T Cytosine C Guanine G Complimentary strands C pairs with G A pairs with T If we know one strand we know the complimentary strand DNA Replication Semiconservative Replication Produces molecules with both old and new DNA but each molecule contains one complete old and one complete new strand Due to complimentary pairing information of strands is rarely lost Helix unzips original strand breaks bonds between nucleotides and enzymes work together to bring new nucleotides to parental chain amp form daughter strands DNA Polymerase matches existing nucleotides on parental chain with complimentary bases amp form bonds between the new pairs DNA is more than just a long strand of genes Each gene codes for a protein or enzyme that operates organism DNA is master instruction manual for the cell Copies of needed portions are madesingle stranded copies of DNA called RNA RNA leaves nucleus to instruct other organelles to make proteins which then go to where they need to go to operate the cell Transcription Process of copying DNA to RNA Replication and transcription occur in the nucleus TranslationRNA to proteins Occurs outside the nucleus RNA Always single stranded Uracil pairs with Adenine rather than Thymine Difference occurs because if RNA is chemically different than DNA you will always know which is the copy Protein Made up of amino acids All proteins are different combinations of only 20 amino acids Codons3letter units that encode amino acids Some codons stop translation The universality of the genetic code is one of the strongest pieces of evidence that all living organisms share a common evolutionary heritage a common ancestorquot
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