Biol 3350 1st Edition Lecture 12 Outline of Last Lecture I. What is natural selection?II. Deviations from Hardy-Weinberg EquilibriumIII. Measuring natural selectionIV. Differential survivalV. Differentiation fecundityVI. Absolute fitnessVII. Relative fitnessVIII. Change in allele frequency due to selectionOutline of Current Lecture I. Outcomes of Natural SelectionII. Selection in natural populationsa. ADH is Drosophilab. Desert sand and nearby ancient lava flowsIII. OverdominanceIV. Cystic FibrosisV. UnderdominanceVI. Mutation as a force of evolutionVII. Modeling mutationa. Irreversible mutationsb. Reversible mutationsc. EquilibriumVIII. Most mutation are deleteriousCurrent LectureI. Outcomes of Natural Selectiona. Outcome is determined by fitness differencesb. Directional selection for A1A1i. A1A1 homozygote has highest fitnessii. HWE is reached when p hat = 1c. Directional selection for A2A2i. A2A2 homozygote has highest fitnessii. HWE is reached when p hat = 0iii. A1 will decrease until it becomes extinct because A2 has the highest fitnessThese 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.iv. When p hat equals 0.0, allele A1 is lost from the populationII. Selection in natural populationsa. ADH is Drosophilai. Fruit flies rely on sugars so they must break down ethanol in order to use the sugarsii. In the control situation, there was no selective pressure for a quicker ability to degrade ethanol (basically a flat line)iii. When raised in the ethanol environment, the frequency of the fast allele rose to fixation in a short amount of time (only 50 generations; strong selection pressure)b. Desert sand and nearby ancient lava flowsi. Light colored mice coats have much higher light reflectance ii. Heterozygous condition has a little bit higher reflectance than homozygous dominant iii. They looked at genotype and allele frequencies in different populationsiv. Shaded area on the graphs are the lava flows where the substrate is very blackv. Frequency of dominant allele was nearly at fixation at these dark sitesvi. Frequency of heterozygous mice was the lowest at the lava sites à the extra amount of reflectance at lava sites made it easier for the predator (owls) to select against themvii. The last graph is of a neutral gene that is not affecting coat color – serves as a control group to show that these differences that she saw were the result of differences in coat color causing differences in allele frequenciesviii. In lava site – homozygous dominant was favor; but this was reverses in sandy soilIII. Overdominancea. A1A2 heterozygote has highest fitnessi. Both alleles remain in the population over timeii. The less fit genotypes stay in the population because need parents of twohomozygotes in order to produce heterozygotesiii. Still have genotypes that are not the most fit maintained in the population due to the overdominanceIV. Cystic Fibrosisa. Cystic fibrosis – lung disease that caused people who are homozygous cause these people to have huge lung infectionsb. Stays in population because people who are heterozygous are resistant to bacterium that causes typhoid feverc. Advantage is to be heterozygous for this mutation b/c don’t get cystic fibrosis andis resistant to typhoid feverd. Cystic fibrosis gene allele frequency is higher in areas where typhoid fever is commone. Mean population fitness is highest when the allele frequency is 0.6 à reach an equilibrium when allele A1 is about 0.6f. Heterozygous condition had a higher fitness than either homozygous conditionV. Underdominancea. Both homozygotes have higher fitness than heterozygotesi. Hard for population to maintain both alleles since heterozygote condition is deleteriousii. Equilibrium is unstable – which ever allele ends up above 0.5 will be favorediii. Allele A1 will either go to 0 or 1iv. The mean population fitness is the lowest when allele A1 is at 0.6v. When A1 is low, then A2 will be favored and will go to extinctionvi. When A1 is close to fixation, the equilibrium will go to fixation in the other directionvii. Selection acts on individualsviii. Equilibrium is reached when population wide fitness if at a very low pointVI. Mutation as a force of evolutiona. Mutations create new allelesi. Introduces variation at the level of the geneii. Provides the raw material for evolution to actiii. Rate of accumulation varies according to effectiv. A mutation rate of 0.0001 is extremely high; mutation rate occur at incredibly low valuesv. Very slow change because mutation rate is so low and mutations are usually deleteriousVII. Modeling mutationa. Irreversible mutationsi. Forward mutation onlyii. No back or reverse mutation occurb. Reversible mutationsi. Forward mutations (A to a) at a rate of mu decease frequency of pii. Backward or reverse mutations (a to A) at a rate of v increase frequency of pc. Equilibriumi. Forward mutation rate = backward mutation rateii. P hat is the equilibrium value of allele A11. Backwards mutation rate divided by the total mutation rateiii. Q hat is the equilibrium value of the mutation1. Forward mutation rate divided by the total mutation rateiv. Rate of change is very slow when you are just including mutationsVIII. Most mutation are deleteriousa. Selection works to eliminate these alleles in populationsb. Recurrent mutation continues to introduce these alleles in populationsc. What is the frequency of a deleterious recessive allele at equilibrium?i. Mutation is favoring this recessive allele since mutation is changing A to a ii. Selection pushes frequency of dominant allele to fixation because it is favorediii. Selection and mutation are acting at cross-purposesiv. Dominant homozygous and heterozygous fitnesses have relatively the same fitnessv. The condition that has the lower fitness is the homozygous recessive mutation; p is moving towards fixationd. What is the frequency of a deleterious dominant allele at equilibrium?i. A2 is the mutant alleleii. Mutation favors the mutantiii. Selection favors the original allele because mutations are typically deleteriousiv. Heterozygous condition doesn’t have as high of fitness due to codominance1. Expresses deleterious conditione. Mutation is most effective in increasing q, when q is recessivei. Recessive trait is hidden in the heterozygous condition allowing it to stay in the populationf. Mutation-selection balance maintains deleterious