Evolution of Populations Microevolution Chapter 23.

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  • Evolution of Populations MicroevolutionChapter 23

  • Micro- EvolutionNatural selection typesSexual selectionMicroevolutionHardy Weinberg ConditionsGenetic driftBottle neckFounder effect

  • Charles Darwin

  • MicroevolutionSlight changes in gene frequencies between generationsPopulations change, not individualsExample:Antibiotic resistance

  • less than 1 in 1,6001 in 400-1,6001 in 180-4001 in 100-1801 in 64-100more than 1 in 64Distribution of malaria cases in Africa, Asia, and the Middle East in the 1920sFrequency of people with the sickle-cell trait

  • Hardy WeinbergUnder these conditions, populations do not change No EvolutionNo mutationsRandom MatingNo Natural SelectionNo Gene FlowLarge Population Size

  • G.H. Hardy 1877-1947

  • Wilhelm Weinberg 1862-1937

  • Hardy WeinbergEquation looks at individual traits, one at a time p & q are allelesProbably couldnt meet the conditions for all traits at once for long.Evolution probably always working at some level.Shows us the factors that alter a populations genepool- evolution.

  • PopulationAll the individuals of the same species in a given location at a given timeThe potentially interbreeding groupThe basic unit of evolutionPopulations evolve, not individuals

  • Fig. 23-5Porcupine herdPorcupineherd rangeBeaufort SeaNORTHWESTTERRITORIESMAPAREAALASKACANADAFortymileherd rangeFortymile herdALASKAYUKON

  • Gene flowAllows gene to move between populationsimmigrationAny new trait arising in one population can move to othersKeeps species together as a interbreeding unit.Blocking gene flow helps form new species.

  • Fig. 23-313.1719XX10.169.128.1112.43.145.1867.159.1012.1911.1213.1715.

  • Fig. 23-12NON-MINESOILMINESOILNON-MINESOILPrevailing wind directionIndex of copper toleranceDistance from mine edge (meters)70605040302010020020020406080100120140160

  • Microevolution in humans: Populations became isolated for several thousands of yearsSlight morphological changes came about by natural selection by climate:Skin tone and sunlight (uv ,vitamin D, Folic acid)Eye shape and winds, and ice etc.Height in some populations.

  • Gene flow and human micro- evolutionIsolated populations now coming back together sharing traits

  • Fig. 23-15

  • Sexual Selection

  • Fig. 23-16SC male graytree frogFemale graytree frogLC male graytree frogEXPERIMENTSC sperm Eggs LC spermOffspring ofLC fatherOffspring ofSC fatherFitness of these half-sibling offspring comparedRESULTS1995Fitness Measure1996Larval growthLarval survivalTime to metamorphosisLC betterNSDLC better(shorter)LC better(shorter)NSDLC betterNSD = no significant difference; LC better = offspring of LC malessuperior to offspring of SC males.

  • Sexual DimorphismSexual selection results in the males and females having different morphology, at least in breeding season.Size elephant seals, primatesColor- bird plumage

  • Genetic DriftRandom events in a small population can alter the genepool. Does not increase fitness.

  • Fig. 23-8-3Generation 1CW CW CR CRCR CWCR CRCR CRCR CRCR CRCR CWCR CWCR CWp (frequency of CR) = 0.7q (frequency of CW ) = 0.3Generation 2CR CWCR CWCR CWCR CWCW CW CW CW CW CW CR CRCR CRCR CRp = 0.5q = 0.5Generation 3p = 1.0q = 0.0CR CRCR CRCR CRCR CRCR CRCR CRCR CRCR CRCR CRCR CR

  • AA in five populationsallele A lostfrom fourpopulations1.00.5015051015202530354045Generation (25 stoneflies at the start of each)In small populations, random deaths influence outcome, by fixing or eliminating alleles.

  • allele A neitherlost nor fixed in large population1.00.5015051015202530354045Generation (500 stoneflies at the start of each)

  • Special cases of genetic drift:Bottleneck a large population reduced by disaster. A few survivors re-grow the population, but with much less diversity.Founder effect a small population colonizes a new area. Who is in the small population affects the genepool of the new population.

  • phenotypes of original populationphenotype of island populationA seabird carries a few seeds, stuck to its feathers, from the mainland to a remote oceanic island.

  • Fig. 23-10Numberof allelesper locusRangeof greaterprairiechickenPre-bottleneck(Illinois, 1820)Post-bottleneck(Illinois, 1993)Minnesota, 1998(no bottleneck)Nebraska, 1998(no bottleneck)Kansas, 1998(no bottleneck)Illinois19301960s1993LocationPopulationsizePercentageof eggshatched1,00025,000
  • Types of Natural Selectionweeds out less fit traits. Reduces genetic diversity in population.Adaptive evolutionDirectional Selection favors one extreme traitStabilizing Selection favors the most common form of a traitDisruptive Selection favors the extremes, often forming disjunct populations.

  • Fig. 23-14(a) Color-changing ability in cuttlefish(b) Movable jaw bones in snakesMovable bones

  • Fig. 23-13Original population(c) Stabilizing selection(b) Disruptive selection(a) Directional selectionPhenotypes (fur color)Frequency of individualsOriginalpopulationEvolvedpopulation

  • Directional selection

  • Directional Selection modifies Beak depth during drought periods

  • Range of values at time 1Number of individuals Stabilizing Selection

  • percent of population2015105birth weight (pounds)1007050302010532percent mortalityStabilizing selection

  • Range of values at time 1Number of individuals Disruptive Selection

  • Galapagos FinchesSpecialization to different feeding sources may have diversified the species.

  • Diversifying selection lead to two beak depths in Cameroon finches

  • 102030405060Number of individuals1012.815.718.5Widest part of lower bill(millimeters)nestlingsdrought survivors

  • Frequency Dependent SelectionRight-mouthed1981Left-mouthedFrequency ofleft-mouthed individualsSample year1.00.50828384858687888990

  • EcotypesLocally adapted populations.Local weather or other conditions selects for adaptations.Still one species, but distinguishable from other ecotypesWhen distributed along a gradient (elevation, north to south) form a cline.

  • Fig. 23- (21C)Latitude (N)MaineCold (6C)Ldh-B b allele frequency

  • A cline:

  • All made by Artificial Selection from wild mustardArtificial Selection: human designed breeding of plants and animals for desired traits by selecting which individuals get to reproduce.

  • Polymorphism

  • Dont confuse:PolymorphismSexual Dimorphism Ecotypes - Cline

  • Fig. 23-1702.5%Distribution ofmalaria caused byPlasmodium falciparum(a parasitic unicellular eukaryote)Frequencies of thesickle-cell allele2.55.0%7.510.0%5.07.5%>12.5%10.012.5%

  • Fig. 23-UN2Sampling sites(18 representpairs of sites)Salinity increases toward the open oceanNLong IslandSoundAllelefrequenciesAtlanticOceanOther lap alleleslap94 allelesData from R.K. Koehn and T.J. Hilbish, The adaptive importance of genetic variation,American Scientist 75:134141 (1987).ESW12345910678111111023456789


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