Chapter 16

Chapter 16

Chapter 16Population Genetics and Speciation

Section 1 Vocabulary PretestPopulation GeneticsMicroevolutionGene PoolAllele FrequencyPhenotype FrequencyTotal genetic information in a populationPortion of gene copies of a given alleleStudy of the frequency and interaction of alleles and genes in populationsChange in the collective genetic material of a populationRatio of individuals with a given phenotype to the total population

Answer KeyPopulation GeneticsCMicroevolutionDGene PoolAAllele FrequencyBPhenotype FrequencyE

Population GeneticsPopulation Genetics is the study of evolution from a genetic point of view (it is the study of microevolution)Microevolutiona change in the collective genetic material of a populationPopulationmembers of the same species that can interbreed. It is the smallest unit in which evolution occurs.

http://www.abc.net.au/science/news/enviro/EnviroRepublish_1417697.htmVariationPopulations show natural variety within a species.Many quantitative traits (height and weight etc.) follow a bell shaped curve.

http://www.bulbnrose.org/Heredity/Mather/poly1.jpgCauses of VariationEnvironmental factorsamount of food, quality of food, etc.Genetic factorsMutationsrandom changes in genesRecombinationreshuffling of genesRandom pairing of gametesGene PoolGene pool total genetic information available in a population

http://www.cartoonstock.com/lowres/rde3053l.jpgAllele and Phenotypic FrequencyAllele frequencyexpressed as a percent: it is determined by dividing the number of a certain allele by the total number of alleles of all types in the populationPhenotypic frequencyexpressed as a percent: it is the number of individual with a particular phenotype divided by the total number of individuals in the population.

Hardy-Weinberg Genetic EquilibriumDeveloped by Wilhelm Weinberg (German physician) and Godfrey Hardy (British mathematician)

http://anthro.palomar.edu/synthetic/synth_2.htmGodfrey HardyWilhelm WeinbergStates that genetic frequencies in a population tend to remain the same from generation to generation unless acted on by outside influences.It is based on a hypothetical population that is not evolving.

http://www.cartoonstock.com/directory/h/human_evolution.aspConditions of Hardy-Weinberg EquilibriumIn Genetic Equilibrium:No net mutations occurPopulation size remains constantThe population is infinitely largeIndividuals mate randomlySelection does not occur

This flock of mallards probablyviolates some or all of the conditions necessary for the Hardy-Weinberg genetic equilibriumhttp://mariewinnnaturenews.blogspot.com/2007_11_25_archive.htmlIt is highly unlikely that all five of the conditions in the Hardy-Weinberg Model will happen in the real world.Therefore, Genetic Equilibrium is impossible in nature.It is a theoretical state that allows us to consider what forces could disrupt such balance (equilibrium). Section 2 Vocabulary PretestImmigrationEmigrationGene FlowGenetic DriftSexual SelectionStabilizing SelectionDisruptive SelectionDirectional SelectionIndividuals move outIndividuals move inChoice of mates based on favorable traitsGenes move from one population to anotherAverage trait is selectedOne extreme trait is selectedTwo extreme traits are selectedAllele frequencies change randomlyAnswer KeyImmigrationBEmigrationAGene FlowDGenetic DriftHSexual SelectionCStabilizing SelectionEDisruptive SelectionGDirectional SelectionF

Disruption of Genetic EquilibriumDisruptions to the Hardy-Weinberg equilibrium can result in evolution.The five requirements for genetic equilibrium can be disrupted by the following outside forces:MutationGene FlowGenetic DriftNonrandom MatingNatural SelectionRequirement #1: No Net Mutations OccurMutations occur constantly at very low rates under normal conditions.Exposure to mutagens (mutation-causing agents, i.e. radiation and chemicals) can increase mutations rates.Mutations produce new alleles for a traitThey can be harmful, harmless or helpfulHelpful mutations are a vital part of evolution.Requirement #2: Population Size Remains Constant Individuals enter and leave populations constantly. Their genes move with them. This is called Gene Flow.Factors influencing gene flow include:Immigrationmovement of individuals into a populationEmigrationmovement of individuals out of a populationMigration and dispersal patterns can also influence the movement of individuals into new populationsBirth and Death Rates also remove or add genes from individuals to a population.Requirement #3 Population is Infinitely Large In nature, population sizes are restricted rather than infinitely large.Genetic Drift can occur in small populations of organismsGenetic Driftthe random change in allele frequency in a populationSignificant changes can happen in small populations if even a single organism either fails to reproduce or reproduces too much.

If the frequency of an allele reaches zero in a population, then (assuming you started with two alleles), there is only one left. All individuals will be homozygous for that trait---creating no variations. This weakens a species.Ex: Northern Elephant Seal

Homozygous for every gene testedhttp://en.wikipedia.org/wiki/File:Northern_Elephant_Seal,_San_Simeon2.jpgBottleneck EffectGenetic Drift can lead to a bottleneck effect in which variations are reduced overtime.

http://biology.unm.edu/ccouncil/Biology_203/Summaries/PopGen.htmRequirement #4: Random MatingsOrganisms do not mate randomly in nature.Mate selection is influence by:Geographic proximitychoose mates nearby: can result in kinship matingAssortative Matingchoose mates with similar traits: reduces variationSexual Selectionchoose mates based on favorable traits

http://upload.wikimedia.org/wikipedia/commons/5/51/Oregon_zoo_peacock_male.jpgRequirement #5: Selection Does Not OccurNatural Selectionorganisms with favorable traits are more likely to survive and reproduce, passing on their favorable genes to the next generation.It is an ongoing process in nature and an important disruption to equilibrium.Three patterns of Natural Selection:Stabilizing Selection: individuals with the average form of a trait have the highest fitness.Ex: Lizard body size

http://upload.wikimedia.org/wikipedia/commons/c/c6/Selection_Chart.PNGDisruptive Selection: individuals with either extreme variation of a trait have the highest fitness.Ex: Shell Color of Limpets

http://upload.wikimedia.org/wikipedia/commons/c/c6/Selection_Chart.PNGDirectional Selection: individuals with one extreme of a trait have the highest fitnessEx: Nose and tongue lengths of anteaters

http://upload.wikimedia.org/wikipedia/commons/c/c6/Selection_Chart.PNGSection 3 Vocabulary PretestSpeciationGeographic IsolationAllopatric SpeciationReproductive IsolationSympatric SpeciationGradualismPunctuated EquilibriumA slow change in a species over millions of yearsBursts of rapid changeFormation of a new speciesPhysical separation of populationsInability to mate or produce offspringSpeciation resulting from geographic isolationSpeciation resulting from reproductive isolationAnswer KeySpeciationCGeographic IsolationDAllopatric SpeciationFReproductive IsolationESympatric SpeciationGGradualismAPunctuated EquilibriumB

SpeciationSpeciationformation of a new speciesSpecies: a single kind of organism whose members are morphologically similar and can interbreed to produce fully fertile offspring.Two types of speciation: Allopatric Speciation and Sympatric Speciation

Allopatric SpeciationAllopatric Speciation: species arise as a result of geographic isolation. (Allopatric = different homelands)Geographic Isolationphysical separation of members of a populationGene flow between the new subpopulations stops and the two begin to divergeEventually, they become incompatible for mating, creating new species.Debate exists as to whether or not allopatric species are different enough to be considered new species.

http://cas.bellarmine.edu/tietjen/images/geographic_isolation.jpghttp://evolution.berkeley.edu/evosite/history/images/geog_isolation.gifExamples of Geographic IsolationSympatric SpeciationSympatric Speciation occurs when two subpopulations become reproductively isolated within the same geographic area.Reproductive Isolationthe inability of members of the same species to mateCan be caused by disruptive selectionTwo types: prezygotic isolation and postzygotic isolation Prezygotic (premating) isolation: (different mating seasons, different mating calls, etc.)

Behavioral Isolation

Habitat IsolationTemporalIsolationMechanical IsolationGameticIsolationOther Prezygotic Isolation Mechanismsinclude Postzygotic (postmating) isolation: offspring do not fully develop, die, or are infertile.

Hybrid is weak and likely to dieHybrid is sterile

http://www.geo.arizona.edu/Antevs/nats104/SymptrcSpctnSml.jpgRates of SpeciationTwo Theories: Gradualism slow change over millions of years Punctuated Equilibriumshort bursts of rapid change

http://bioap.wikispaces.com/file/view/gradualism.gif/94608242/gradualism.gifEvidence exists that suggests that both have taken place over time.

http://silvertonconsulting.com/blog/wp-content/uploads/2010/06/c7-1-23-finches.jpghttp://www.doctortee.com/dsu/tiftickjian/cse-img/biology/evolution/horse-evolution-2.jpgThe Hardy-Weinberg EquationHardy and Weinberg went on to develop an equation that can be used to discover the probable genotype frequencies in a population and to track their changes from one generation to another.The equation is: p2+2pq+q2 = 1

p= frequency of the dominant allele q = frequency of the recessive alleleSee handoutSignificance of the Hardy-Weinberg EquationPunnett Squares allow geneticists to predict the probability of offspring genotypes for particular traits based on the known genotypes of their two parents The Hardy-Weinberg equation essentially allowed geneticists to do the same thing for entire populations.Before Hardy and Weinberg, it was thought that dominant alleles must, over time, wipe out recessive alleles (genophagy = gene eating)According to this wrong idea, dominant alleles always increase in frequency from generation to generation.Hardy and Weinberg demonstrated that dominant alleles can just as easily decrease in frequency.