BIOB 272 1st Edition Lecture 20Outline of Last Lecture Population Genetics (Migration)I. Darwin’s PostulatesII. Examples of Natural Selection III. Natural Selection and H-W AnalysisIV. Natural Selection is Differential FitnessV. How to Calculate Mean Fitness and Genotype FrequenciesVI. Directional SlectionVII. Heterozygous Advantage- Sickle Cell Anemia- MalariaOutline of Current Lecture Population Genetics (Migration)I. Sickle-cell and Malaria Continueda. Heterozygous AdvantageII. Extreme Changes in Population Sizea. Population Bottlenecksb. Founder EffectsIII. Small Population EffectsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.a. Inbreedingi. Hapsburg DynastyIV. Population Genetic StructureV. Mathematical Model of Gene FlowVI. Gene Flow EffectsVII. MigrationVIII. Migration and DrifCurrent LecturePopulation Genetics (Migration)I. Sickle-cell and Malaria Continued- Sickle Cell Diseaseo Highly Pleiotropico Untreated= lifespan is 20-40 yearso Treatment lifespan= 50s and beyond- Malaria:Plasmodium falciparumo 3.3 billion people at risk of malariao 250 million malaria cases per yearo one million deaths per yearo in Africa, 1 in 5 childhood deathso Every 30 seconds a child dies from malaria- Heterozygous Advantage= example is sickle-cell anemiao w11< w12 > w22o Both alleles maintained by selectiono Neither allele fixes (p or q=1), rather they settle on an equilibrium frequencyII. Extreme Changes in Population Size: Single sampling of founders for new populationN decreases in bottleneck, then increases againa. Population Bottlenecks:- Bottlenecks reduce genetic variation- Bottleneck increases genetic drifb. Founder EffectsIII. Small Population Effectsa. Inbreeding: mating between relatives- higher chance in small populations- Has direct negative effects on fitness (inbreeding depression) by increasing homozygosity of harmful recessive alleles- Leads to a loss of genetic diversity and less opportunity for adaptive evolution- Hapsburg Dynasty=lots of inbreeding- Inbreeding coefficient: probability that two alleles are identical by descentIV. Population Genetic Structure:- So far, we have mainly been concerned with panmicticpopulations (large, random mating)- However, species usually are not large randomlymating groups.- Most species consist of many local populations,or demes, that are moreor less isolatedfrom one another.- Population, any group of conspecific individuals (i.e.,populations are ofen nested within largerpopulations)- Deme, a local random mating population- Migration = gene flow = genetic exchange betweenpopulations or demes- Population Structure: Our group of desert toads consists of 2 demeswhich display different allele (and thus genotype)frequencies- Each deme exhibits random mating- But mating within entire group is non-random:genotype frequencies of entire group wouldnot match HW expected proportionsV. Mathematical Model of Gene Flow: m = proportion of individuals in the deme that havemigrated into it that generation*- Just focus on one recipient population for migrationVI. Gene Flow Effects- Gene flow makes demes more genetically similar- Over multiple generations allele frequencies converge on p*, equilibrium value where net changep= 0- 2 Main Effects:1. Gene flow reduces genetic differences betweenpopulations.2. 2. Gene flow increases genetic variation withinpopulations.VII. Migration:- Gene flow homogenizes populations- Impact of migration depends on migration rate (m)- Gene flow can oppose local selection- But gene flow may also introduce adaptive variationVIII. Migration and Drif:- Migration and drif both affect ALL loci (selection only some)- Drif and isolation cause populations to diverge and lose genetic variation - Migration homogenizes populations and increases variation within populations- Gene flow interacts with drif to produce population genetic structure visible at neutral marker loci (many applications inconservation biology)- Together, drif and migration determine population
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