ch 16 evolution of populations

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Ch 16 Evolution of populations. Crash Course: Population Genetics. 16-1 Genetic equilibrium. Population genetics : study of evolution from a genetic point of view Basically how populations of a species evolve But what is a population? - PowerPoint PPT Presentation


Ch 16 Evolution of populations

Ch 16Evolution of populationsCrash Course: Population Genetics Genetic equilibriumPopulation genetics: study of evolution from a genetic point of viewBasically how populations of a species evolveBut what is a population?Group of members of the same species living in the same areaSources of genetic variationThree main sourcesMutations: any change in sequence of DNAReplication mistakesRadiation/environmental causesrecombination: reshuffling of genesRandom pairing of gametes

Bell curveMany traits in nature show trends like this

Phenotype continuum# of individuals with that traitNumber of phenotypes produced depends on how many genes control that traitSingle gene traits- have two allelesTwo distinct phenotypes

Polygenic traits- controlled by two or more genesResults in multiple phenotypes

Gene pool- all genes, including all different alleles, that are present in a populationfrequency (of an allele)- number of times alleles occur in a gene poolPercentageGenetic definition of evolution?Change in relative frequency of alleles in a population over timePhenotype frequencyHow often a specific phenotype is observed in a populationCan be written mathematically

Frequency = # indiv. w/a particular phenotype total # of indiv. in populationHardy-Weinberg equilibriumWhen evolution is not occurringAllele frequencies remain the sameIn order for evolution to not occur, certain conditions must be met. Evolution Versus Genetic EquilibriumHardy-Weinberg principle = Genetic EquilibriumRandom Mating Equal opportunity to produce offspringLarge Population Genetic Drift does not effect Allele FrequencyNo Movement into or out of Population The gene pool must be kept together (no new alleles)No Mutations Mutations cause new forms of alleles changing the frequencyNo Natural Selection All genotypes must have equal probability of surviving.Hardy-Weinberg equilibriumAllele frequency equation p + q = 1p = frequency of dominant alleleq = frequency of recessive alleleTogether, they make 100% of alleles for a gene in that populationIf p = 34%, what is q?If q = 19%, what is p?0.660.81Hardy-Weinberg equilibriumGenotypic frequency equationp2 + 2pq + q2 = 1p2 = homozygous dominant frequency2pq = heterozygous frequencyq2 = homozygous recessive frequencyIf p = .46, what is p2?If p = .12, what is q2?If q =.31, what is 2pq?0.21160.7744 = 77%0.427816-2 Disruption of genetic equilibriumMutationOccur at a relatively constant rate over timeCan be sped up when exposed to mutagensGene flow: process of genes moving from one population to anotherImmigration: moving into a populationEmigration: moving out of a population

Genetic DriftAlleles can become rare by chanceOver time a series of chance occurrences can cause an alleles to become common in a populationEffects of genetic drift are more dramatic with small population sizeFounder effect: change in allele frequencies as a result of migration of a small subgroup of a population

Sample of Original PopulationFounding Population AFounding Population BDescendantsGenetic DriftSection 16-2

Sample of Original PopulationFounding Population AFounding Population BDescendantsGenetic DriftSection 16-2

Sample of Original PopulationFounding Population AFounding Population BDescendantsGenetic DriftSection 16-2

Nonrandom matingSexual selection: tendency of individuals to choose a mate with certain traits.Common in birdsPeacock displayTropical birds of paradise - Papua New GuineaThe amazing Lyrebird - AustraliaNatural selectionNatural selection on a single gene traits can lead to changes in allele frequencies Natural selection on polygenic traits 3 possible effectsDirectional selectionStabilizing selectionDisruptive selection selectionWhen individuals at one end of curve have higher fitness than individuals in the middle or the other end

Stabilizing selectionWhen individuals near the middle have higher fitness than the individuals at either end

Disruptive selectionWhen individuals at upper and lower ends have higher fitness than individuals near the middle

16-3 Formation of SpeciesAs new species evolve, populations become reproductively isolated from each otherReproductive isolation: when two members of populations cannot interbreed and produce fertile offspringSeparate gene poolsIsolation MechanismsGeographic Isolation:- separation of animals in a specific region- formation of river, canyon, mountain

Isolation MechanismsBehavioral Isolation:- differences in courtship or reproductive behaviors-meadowlark songs

Temporal isolation:-two or more species reproduce at different times-orchidsFormation of speciesAllopatric speciation: when species arise from geographic isolationDifferent places

Reproductive isolationPrezygotic isolation: premating isolationSpecies may live in different placesReproduce at different timesHave different mating behaviorsPostzygotic isolation: postmating isolationHybrids may be weakHybrids may be sterile

Sympatric speciationSympatric speciation: when two subpopulations become isolated while living in the same area

Rates of speciationGradualism: speciation at gradual and regular rate

Punctuated equilibrium: periods of sudden, rapid change followed by periods of littelchange