ZOOL 4133 1st Edition Lecture 4 Selection, mutation and Hardy-Weinberg I. Natural selection is a mechanism that is the driving force for evolutiona. Evolution needs heritable genetic variationb. Mutation = source of new genetic variationc. Population genetics combines population variation with geneticsd. gave evolution a mathematical basisII. What processes can cause changes in allele frequencies in a population?- mutation- selection- migrationo gene flow between populations- genetic driftIII. a null model in population geneticsa. model makes the following assumptions:i. “no selection ii. no mutationiii. no migrationiv. no genetic driftv. random mating”b. population of mice calculation examplei. calculate allele frequencies in current populationii. predict genotypic frequencies in the next generationIV. calculating allele frequenciesa. count alleles i. i.e. A=120 a=80 total = 200b. calculate the frequency of each i. always adds up to 1ii. A = .6 a=.4c. count genotypes i. AA=.36ii. Aa=.48iii. aa=.16V. Predicting genotypic frequenciesa. allele frequencies in general population 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.i. A = 0.6 a=0.4b. calculate the probability of observing each genotype in offspring generation i. Genotypeii. AA .6 x .6 = .36iii. Aa .6x .4 = .48 iv. aA v. aa .4 x.4 = .16c. sum = 1 i. no evolutionVI. Hardy-Weinberg equilibriuma. p^2+2pq=q^2= 1b. in an idealized population where there is no:i. “no selection ii. no mutationiii. no migrationiv. no genetic driftv. random mating”c. for allele frequencies p and q, the genotype frequencies: p^2+2pq=q^2= 1 after one generation with random matingd. allele frequencies remain steady with each generatione. purpose: to have a clear, numerical estimate for the null hypothesisVII. No selectionf. all members ofg. Ex:i. B1 = .6 B2=.4ii. number of zygotesiii. add in selectioniv. heterozygote - lose 25%v. homozygote- lose 50%h. # individual/genotypei. X10 gametes/individual combined to gene poolj. final allele frequenciesi. smaller #/bigger #k. if final #s are not the samel. Hardy-Weinberg does not hold m. allele frequencies do not stay the same for each successive generationn. example in notes is extremely strong selectiono. predicting allele frequencies - until frequency = 1p. chart in notesVIII. you can vary selectiona. it's going to take longer with deeper selectioni. over time the frequency of the B1 allele is going to rise above the B2 alleleIX. allele frequency change under selectiona. example from lab - Drosophilab. start out in a pop of flies - looking at change in frequency of F(allele)c. experimental group - exposed to ethanoli. over generation (50 gens) frequency of ADHF allele rises and fixes1. Is thought to do a more efficient job of breaking down alcoholii. allele frequencies are not constant from generation to generation1. why?a. genetic drift (random)i. random selection errorX. flower beetlesa. there’s an allele that is lethal when it's in the homozygous stateb. double lethal allele = deadc. starting allele frequenciesi. 0.5 of eachd. How will the frequency of the lethal allele change across generations?i. experimenters are not selecting for any specific trait; letting lethal allele act on its owne. one generation of random matingi. H-W tells us that: they will all be deadf. each survivor contributes 10 gametes to the gene poolg. decrease in recessive lethal alleleh. increase in viable allelei. this happens because fewer are dying with each generation1. based on the expectations of selectionii. population started out will all heterozygotes and they're finei. rare recessive variants are really important in studying human diseasesi. what alleles encode these rare variantsXI. Overdominacea. Heterozygotes have higher fitness than both classes of homozygotesXII. underdominancea. heterozygote disadvantageb. both classes of homozygotes have higher fitnessXIII. frequency-dependent selectiona. orchidsb. flower color polymorphismi. purple, yellowc. both colors attract beesd. neither one provides a nectar rewarde. Why do both false advertisements persist in nature?i. bees looking for nectar alternate between yellow and purple flowersii. whichever color is less common will get more bee visits (pollination)f. H2: color polymorphism maintained by selection by rare phenotypeg. reproductive success of yellow vs purplei. H2ii. bees have a slight preference for yellowh. Allele frequency change with mutationi. in an idealized population where there is no:i. “no selection ii. no mutationiii. no migrationiv. no genetic driftv. random mating”XIV. mouse populationa. starting with alleles A=.9 and a=.1i. no selectionb. what happens with random mating, no selection, but yes to mutationc. H-Wi. .81 for homoii. .18 for heteroiii. .01 for other heterod. add mutation:i. 1/10000 in every A alleles mutates to aii. frequencies after mutation1. A =0.9 - (0.9/10000) = 0.899912. a= 0.1+ (0.9/10000) = 0.10009e. it doesn’t do a lot across a few generationsf. across many generations, if same mutation rate, gradually decrease the frequency of big A allelesi. slow change isn't the same as no