1Bio1B Evolution 5Last lecture:• Predicting genotype freq’s: Hardy (Castle) Weinberg Equilibrium– Application: Predicting heterozygote frequencies for recessive traitsEvolutionary processes• Sampling effects => “genetic drift”– Relevance in evolution - loss of variation, bottlenecks• Mutation as the ultimate source of variation; effects on fitness• Migration (as gene flow)TodayEvolutionary processes• Migration and genetic clines• Selection– Fitness– Forms of selection– Heterozygote advantage - eg. sickle cell anaemia– Directional selection - eg. coat color in mice; genome signatures,experimental evidence2Migration (asgene flow)• Gene flow = movement ofgenes among populations• Arises from net movementbirth -> reproduction orgamete dispersal ->zygotes• Spreads new mutations;maintains variation• Opposes effects of geneticdrift or local selection• Spread of genes fromGMO crops is a concern3Genetic fitness• Selection acts throughthe phenotype• Fitness = Survival andreproduction relative toother phenotypes orgenotypes in thepopulation• Relative fitness can beenvironment dependentSorry Arnie….4Forms of selection (Fig. 23.13)5Relative fitnesses:Without malaria:HbbAA > HbbAS > HbbSSanaemiaWith malaria:HbbAS > HbbAA > HbbSSExample of Heterozygote advantagesickle-cell anaemiaMoreresistantto malariaNote - fitness of HbbAS depends onenvironment (+ malaria)67Association between melanicphenotype and Mc1r allele in rockpocket mice from Pinacates lava flowHopi Hoekstra inthe field..Geographic cline8Agouti melanisticmutations:Recessive [regulatory& coding]Mc1r MelanisticmutationsDominant[structural]So what? … Mc1r & melanoma!XSome key genes in melanin production pathway9Experimentalevidence forrapid evolutiondue to selectionEg. guppy color -field experiments;text pp460)• Others - microbialevolution etc etcFig. 22.1310Genomic signatures of recent selectionNew mutation arisesthat increases fitnessUnder directional selectionincreases to p = 1; dragslinked sites with itResults in a region of lowvariation relative to othersVariationVariable sitehigh highhighlowStorz 200511Genomicsignatures ofselection;localizedreductions indiversitySutter et al. 2007Science 316:112What’swith mycrazy
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