BIOL 201 1st Edition Lecture 4Outline of Previous LectureI. Darwin’s theory of Evolution by Natural SelectionII. Antibiotic ResistanceIII. Selection & the Hardy-Weinberg equilibriumIV. Fitnessa. Computing fitnessV. Adaptive landscapeVI. Selectiona. For recessive allelesb. For dominant allelesc. For codominant allelesVII. Change in allele frequency due to selectionVIII. When evolution is fastIX. Maintenance of Polymorphisms a. Temporal fluctuationsb. Spatial fluctuationsc. Inverse frequency-dependent selectionOutline of Current LectureI. Self-incompatibility in plantsII. Heterozygote Advantagea. Sickle CellIII. Alternative equilibriaa. Positive frequency-dependent selectionb. Heterozygote disadvantageIV. Selection and Quantitative TraitsV. 3 modes of Selectiona. Directional Selectionb. Stabilizing Selectionc. Disruptive SelectionVI. Detecting Selectiona. Correlation across populationsb. Comparing survivors to non-survivorsc. Functional selectiond. Convergent Evolutione. Molecular methodsVII. Measuring selection and responses to selectiona. Selection differentialb. Response to selectionc. Connecting the two + heritabilityd. Selection gradientCurrent LectureI. Self-incompatibility in plants: i. sometimes plants have hundreds of alleles present at lociii. Plants are incompatible with alleles that they already have in order to maintain variationiii. Rare alleles have mating advantage because they can mate withmore of the populationII. Heterozygote Advantage : also called Overdominance, tends to maintain polymorphisms. i. If you lose allele little a, the highest fitness of the heterozygote will keep little a alive. Rare trait will be maintained.b. Sickle Cell: example, having the sickle cell little c allele are resistant to malaria resistant so have higher fitness.i. Heterozygotes don’t have the full phenotype of sickle cell but not as bad as cc  heterozygote advantageii. Frequency of sickle cell is higher in areas with more malaria present because of resistance provided by presence of alleleIII. Alternative equilibria: flip side of maintenance of polymorphisma. Positive frequency-dependent selection: favoring the more common allele in selectioni. Aposematic coloration: warning color in animals1. Prey are sending signal to predator that they’re not good prey. Most are toxic or just a bad idea to chase.2. Predators are more likely to randomly sample the rare colors because they’ve learned to avoid the more common warning colored animals.b. Heterozygote disadvantage: happens when either homozygote is good for fitnessi. Fitness of homozygote could be different as long as they’re higher than the heterozygote.ii. A or a is fixed. Have to know which is more common to determine which one will be fixed. IV. Selection and Quantitative Traitsi. Quantitative traits are continuous like height and weight.ii. No longer use Hardy-Weinberg proportionsV. 3 modes of Selectiona. Directional Selection: most common form, evolution of the mean of a population in one directioni. Probability of survival is higher for one extreme of the scale of traitsii. The mean has shifted after selection. If favor the higher side then mean will move up.iii. Start looking at graph of all in population and then look at graph of survivors of selectionb. Stabilizing Selection: highest probability of survival is around the mean and drops at either side of meani. Reduces the variance of the population ii. Ex: birth weightc. Disruptive Selection: rarest of the 3, opposite of stabilizing, probabilityof survival is greatest at extremes of distribution and lowest in the middlei. Retain numbers of extremes but lower bars for the mean and around the meanii. No change in the mean but there’s an increase in varianceVI. Detecting Selection: can’t use Hardy-Weinberg anymorea. Correlation across populationsi. Ex: Bergmann’s rule= the further north from the equator, the larger the body size of many species and vice versa. Probably has to do with climate changes.b. Comparing survivors to non-survivors: do so graphically to determine the type of selection acting on populationi. Flat graph: no selection acting on populationc. Functional selectioni. Ex: enzyme activity in fish (Antarctic vs. tropical); see that enzyme activity is better at warmer temperatures for the tropical fish and at lower temperatures for the Antarctic fishd. Convergent Evolution: similar phenotypes of different species who don’t live close to each other, converged to similar phenotypes due to similar environmental nichese. Molecular methods: look at gene sequences and look for departures from what’s expectedVII. Measuring selection and responses to selectiona. Selection differential: Si. S= t* - average tii. Difference in means after selection vs. before selectioniii. Average t (with bar over it usually) is the average before selection while the t* is the average after selection (within that generation/no reproduction yet)iv. S can be negativeb. Response to selection: Ri. R= h2Sii. h2= heritability and adds the reproduction to the processc. Connecting the two + heritabilityi. To get the average adults before a second generation, you add Rto the average from the initial generationii. If there is a good correlation between the midparent and midoffspring phenotype then the heritability will be 1. all ofS get’s transmitted into R so all of the variation and phenotypic change is translated into the next generationiii. When heritability is less than 1, R is less than S and the variation is diluted by low heritabilityiv. Means are also a lot closer between the 2 generations v. No heritability means no change due to selection and you need a high heritability to get a high selection responsed. Selection gradient: slope of regression of relative fitness on a phenotype/character; another way to measure selection; gives sense of how fit you are based on your phenotypei. Selection gradient= Beta = S/Pii. Heritability = G/P and P= VP; G= additive genetic variationiii. R= delta zaverage =