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Lecture 13

Lecture 13- selection and fitness .docx

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Biology 1001A
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Lecture13SelectionandfitnessMeaning of deme population allele frequency genotype frequencyDeme a local population of organisms or one species that interbreed with one another and share a distinct gene poolPopulation made up of 2 major attributes allele frequencies and gene pool a group of sexually interbreeding or potentially interbreeding individualsAllele frequency the frequencies of individuals alleles do not depend on genotype frequenciesGenotype frequency dominance or recessiveness Gene pool all the alleles of all individuals in the populationAllele frequencies in a population given the genotype frequenciesAllele frequencies dont depend on genotype frequenciesRemain essentially unchanged from one generation to the next provided that mating is random and all genotypes are viableAllele frequencies are conserved in a population and are in equilibrium given that no external forces act on them Genotype frequencies in the next generation given the allele frequencies and assuming HardyWeinberg equilibriumAfter the first generation genotype frequencies will remain at HardyWeinberg equilibriumTraits remain in equilibrium do not become dilutedThis rarely happens in nature because hardyWeinberg conditions are rarely achievedAssumptions of HardyWeinberg equilibrium founding theorem of population geneticsRandom mating Large populationsEquilibrium allele frequenciesAbsence of gene flow into populationthe expected genotype frequencies in a population can only be calculated using allele frequencies if the population is in hardy2Weinberg equilibriumfAAp fAA2pq1111whether a population is in HWE given observed genotype or phenotype frequenciesif the expected genotype frequencies calculated using given data and the HWE equation is the same as that observed then the population is in HWE effect of selection on changes in allele frequencyif selection pressure is stronger then evolution proceeds more quicklyrelative vs absolute fitnessRelative w relative to other genotypes in the population how fit is that genotype The fittest genotype has a Absolute W how many offspring an organism produces in its lifetime or how long it liveshow to calculate relative fitnesswWWmaxhow to quantify strength of selectionDifference in w between 01 between genotypes reflects strength of selectionfittestrelative fitness of 1 the greater the difference in relative fitness the stronger selection is going to be the faster evolution will proceedRelationship between dominancerecessiveness of alleles and response to selectionSelection against a dominant allele will wipe out all the dominant alleles in a population BUT selection against a recessive allele will not wipe out all the recessive alleles because they are sheltered in the heterozygous form effect of heterozygote advantage on genetic variationheterozygotes preserve the presence of recessive alleles because no matter what selection favors or selects against the recessive allele is always sheltered in heterozygotes and will never be wiped outDominant alleles however may be wiped out because they are not sheltered in either homo or heterozygotesHeterozygote advantage maintains both alleles in a consistent frequency why the amount of genetic variation in a population is importantgenetic variation is the raw material of evolution Without it evolution and adaptability would not happen It is also important for individual fitness example inbreeding creates lower individual fitnessdifferent types of selection stabilizing directional and their effect on genetic variationstabilizing selects against extreme phenotypes increases heterozygotesdirectional selects against one extreme disruptive selects against heterozygotes less variableLecture14Selectionvsotherevolutionarydifference between Batesian and Mullerian mimicryBatesian palatable species that mimic distasteful models are
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