BIOB 272 1st Edition Lecture 19 Outline of Last Lecture Population Genetics (drift)I. Mutation Rates Vary in Sperm vs. Eggs (sex-dependent)II. Mutation SummaryIII. Hardy-Weinberg (H-W) Assumptions- Random Mating- No Mutation- Infinite Population Size- No Natural Selection- No Migration (no gene flow)IV. Genetic Drif- Sampling Error- Two Primary Population Genetic EffectsV. Genetic Drif in ActionVI. Change in Allele Frequencies by Drif- Small Population Size on Genetic DrifVII. Effective Population Size (Ne)VIII. Inbreeding Outline of Current Lecture These 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.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 AnemiaCurrent LecturePopulation Genetics (Migration)I. Darwin’s Postulates1. Individuals vary2. At least some variation is heritable3. Some individuals leave more progeny thanothers4. The variation in survival and reproductionis not random, but depends on heritabletrait variationOutcome:(genetic) variants with higher survival and/or reproduction increase in frequency inpopulationII. Examples of Natural Selection (1) Variation (2) Inheritance(3) Differential survival (4) ResponseIII. Natural Selection and H-W Analysis1. Selection can cause allele frequencies to change from generation to generation2. Selection can cause deviation from H-W genotypefrequencies3. Selection is deterministic (predictable)4. Selection can be a strong evolutionary forceIV. Natural Selection is Differential Fitness Fitness: the reproductive success of an individual with a particular phenotype o Components of fitness: – Survival to reproductive age– Mating success – Fecundity Relative fitness: fitness of a genotype standardized by comparison to other genotypesV. How to Calculate Mean Fitness and Genotype FrequenciesAlleles A1 A2Genotype A1A1 A1A2 A2A2Frequency p^2 2pq q^2Genotype Fitnessw11 w12 w22Mean Fitness of PopulationWbar= p^2*w11 + 2p^2*w12 +q^2w22Genotype Frequencies of surviving individuals(p^2*w11)/wbar (2pqw11)/wbar (q^2*w22)/wbarNew allele frequency for p in the gene pool for next generation:p’ = (p^2 * w11 + pq* w12)/wbarNew allele frequency for q in gene pool for the next generationq’ = (pq* w12 + q^2 * w22)/ wbarExamples With Numbers:Alleles 0.45 0.55Genotype A1A1 A1A2 A2A2Frequency 0.2 0.5 0.3Genotype Survival100% 80% 60%Mean Fitness of PopulationWbar= 0.2*1+ 0.5*0.8+ 0.3*0.6 =0.78Genotype Frequencies of surviving individuals(0.2*1)/0.78=0.26(0.5*0.8)/0.78=0.51(0.3*0.6)/0.78=0.23New allele frequency for p in the gene pool for the next generationp’ = 0.26 + 0.255= 0.515New allele frequency for q in gene pool for the next generationq’= 0.255 + 0.23 = 0.485VI. Directional Slectionw11> w12 > w22• Increases the mean fitness of the population by increasing the frequency of genotypes with higherfitness.• Drives one allele towards fixation(equilibrium allele frequency of p* = 1)example: cycstic fibrosis:•abnormal transport of chloride and sodium across the epithelium inexocrine tissues,leading to thick viscous secretions inthe lungs, pancreas, liver, intestine,and reproductivetractIf directional selection increases w, harmful deleterious alleles are common because natural selection is not very effective at acting on rare recessive alleles because most copies are in heterozygotesVII. Heterozygous Advantage (overdominance) w11< w12 > w22-Both alleles maintained by selection-Neither allele fixes (p or q=1), rather they settle on an equilibrium frequency-With heterozygous advantageand relative fitnesses,w11=0.9 w12=1.00 w22=0.8p*=(w22 - w12) /(w11 - 2w12 + w22)p* = ~0.67- Sickle Cell Anemia: sickling allele for beta hemoglobin due to single point mutationo Highly pleiotropic o If untreated: lifespan 20-40 yearso Treatment 50s or beyond- Malaria: Plasmodium Flaciparumo 3.3 billion people at risk of malariao 250 million malaria cases per yearo one million deaths per yearin Africa, 1 in 5 childhood deathso Every 30 seconds a child dies from
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