BIOB51 - evolution final exam lec notes

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Biological Sciences
Maydianne Andrade

Lecture 9 Genetic Variation Mutation1Genetic variation and selection2Muation and new alleles3Mutation rates4Evolution of mutation rateGenetic Variation and SelectionEvolution cannot occur without heritable variationHistorical view Natural selection eliminates most viariation in populations so little variation present in current populations evolution is a thing of the pastBUT we now know that MUTATION is constantly generating new variantsDoes Mutationkeep up with selectionWe know evolution cannot occur unless there is heritable variation Based on the historical view evolution was the thing of the past we should all be in equlibirum because all the variation would have been removed by nowThis is UNTRUE mutations always creates variation in a population Mutation happens but not at a high rate very rareDoes mutation keep up with selection does mutations generate new variations that new populationsReminderGene section of DNA that codes for a distinct RNA or protein productLocus location of a gene on a chromosomeAlleles versions of the same gene that differ in their base sequenceMutations changes in the base sequence of DNATwo ways to measure genetic variation1Polymorphism Fraction of genes in a population with at least two alleles2Mean Heterozygosity H meanindividuals heterozygous per locus OR Fraction of genes that are heterozygous in genotype of average personMutations are anything that change the base sequence of DNA2 main ways to measure mutationsPolymorphism Fraction of genes in a population with at least two allelesIf you look in this whole room of people and ask how many differnet possibilities are there at any given locus ie locus for salivary amylase how many different alleles are there for salivary amylaseMean Heterozygosity HMeanind Heterozygous per locus ORAre there more than one allele within that locus within that individualFraction of genes that are heterozygous in genotype of avg personAcross their entire genome what proportion of their genes are heterozygousHow are estimates of polymorphism different from estimates of HeterozygosityLoci A and Loci B are the only two genes that these species has that we are looking atBoth of these locis are polymorphic and locus A we have both alleles A and allele a and loci B we have allele B and allele b this means these two locis are both 100 polymorphousHeterozygosity looks the proportion of these individuals that are heterozygous in this case only one of the three individuals are herterozygous and they are heterozygoius at one of the two loci Loci BDont need to know how to calculate heterozygosityBased on allozyme electrophoresis electrophorectic analysis of variation in enzymesMore accurate Examine genetic sequences directlyeg CFTR gene cystric fibrosis transmembrane conductance regulatorBased on gene sequnces analysis15 000 cystic fibrosis patients500 different mutations at this one locus cause the same phenoytypic effect cystic fibrosisCFTR geneMutation that results in cystic FibrosisGenes sequences analysis of over 15000 patientsFrequency histogram showsin a sample of individuals the number of mutations in the gene that results in cystic fibrosisWhat they found that was that there are a number of mutations on the same gene that can cause the same outcomephenotype a lot of variation at this locusExtensive variation in populationsThis variation most comes from point mutationsDozens to hundreds of different alleles are present in most genes for human popultations high polymorphismPoint mutations generate new allelesPoint mutationSinglebase substitution in DNA sequenceOne of the most common sources of genetic variationCan have large effects on phenotypesCauses1Random errors in DNA synthesis2Random errors in repair of damaged sitesEg Sicklecell anemiaSinglebase substitution in hemoglobin genePoint mutationie sickle cell anemiasingle base substitution in hemoglobin geneThose mutations are new alleles new gene sequences that could potentially lead to a new protein productPredicted fate of a new alleles depends on its fitness effectDeleterious Neutral or BeneficialHow does it affect lifetime reproductive success for that individualDeleteriousDecrease reproductive successCan be lost by selectionNeutral Maintained lost or fixedBeneficialIncrease reproductive successMaintained or fixed by selectionHow can mutations be neutral to fitnessSilent site synonymous substitution no change in proteinno change in phenotypeneutralPoint mutation that does not result in an amino acid changeIf base pair change stays within one codon there will b no change due to redundancy of amino acidsReplacement nonsynonymous substitutionPoint mutation changes the codonDifferent amino acid results in the protein changeIf new amino acid results in similar chemical structure the protein may still fold effectively and work properlyNontranscribed regionNot at a locus that is producing a protein product at all then neutralLecture 10Do we expect on average if mutations are deleterious neutral or beneficial Debate in literature right nowIn general we dont expect them to be beneficialIf we have an organism that is adapated to its environemetn and something random happens to change its phenotype in general we do not expect that random change to be beneficial so usually we expect mutations to be deleterious or neutralSea Elegans ExperimentCan sequence most of the genome all genes are known and identifiedReproduces asexually and sexually
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