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BIOL 102 Chp 23: The Evolution of Populations
 

BIOL 102 Chp 23: The Evolution of Populations

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This is a lecture presentation for my BIOL 102 General Biology II students on Chapter 23: The Evolution of Populations (Biology 8E by Campbell et al, 2008). ...

This is a lecture presentation for my BIOL 102 General Biology II students on Chapter 23: The Evolution of Populations (Biology 8E by Campbell et al, 2008).

Rob Swatski, Assistant Professor of Biology, Harrisburg Area Community College - York Campus, York, PA.
Email: rjswatsk@hacc.edu

Please visit my website, BioGeekiWiki, for more biology learning resources: http://robswatskibiology.wetpaint.com

Visit my Flickr photostream for anatomy model photographs!
http://www.flickr.com/photos/rswatski/

Thanks for looking!

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    BIOL 102 Chp 23: The Evolution of Populations BIOL 102 Chp 23: The Evolution of Populations Presentation Transcript

    • Chapter 23The Evolutionof Populations BIOL 102:General Biology II Rob SwatskiAssociate Professor of Biology HACC- HACC-York
    • Overview of Natural Selection Natural selection acts on individuals, but only populations evolve Evolution occurs through genetic variations in populations Ex: Medium ground finch & beak size during2 drought Medium ground finch
    • Microevolution Average beak depth (mm) 10 Microevolution: changes in a population’s allele frequencies over 9 generations Three mechanisms 8 cause allele frequency change: 0 1976 1978 1) Natural selection, (similar to the (after 2) Genetic drift, 3) Gene flow prior 3 years) drought) 3
    • 4
    • 5
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    • Alleles 7
    • Two main sources of gene pool variation: SexualMutation Reproduction 8
    • 9
    • Harold and Maude (1971) 10
    • GeneticVariation Variation in individual genotype leads to variation inindividual phenotype Natural selection can only act on variation with a genetic component Not all phenotypic variation is heritable 11
    • Nonheritable Variation Moth caterpillars raised on oak flower diet resemble oak flowers 12
    • 13 Moth caterpillar siblings raised on oak leaves resemble oak twigs
    • Population variation is the result of: Discrete Quantitativecharacters characters Vary along a Are classified continuum within as “either/or” a population Phenotype is often influenced by 2 or more genes 14
    • DiscreteCharacters 15
    • 16
    • Quantitative Characters 17
    • GenotypesHomozygous HeterozygousIndividual having Individual having 2 of the same 2 different allelesalleles for a given for a given locus locus 18
    • AverageHeterozygosity A measure of gene variability Measures the average % of loci that are heterozygous in a population 19
    • NucleotideVariability Measured by comparing the differences between DNA sequences of pairs of individuals 20
    • 21
    • Drosophila melanogaster Average Nucleotide heterozygosity variability 180 million 13,700 genes nucleotides in genome in genome = 14% (1,920 loci) = 1% (1.8 million) 22
    • Geographic Variation Differences between gene pools of separate populations or population subgroups 23
    • Geographic Variation in Isolated Mouse Populations on Madeira 1 2.4 3.14 5.18 6 7.158.11 9.12 10.16 13.17 19 XX karyotypes 1 2.19 3.8 4.16 5.14 6.7 9.10 11.12 13.17 15.18 XX Isolated populations have differences in fused chromosomes 24
    • ClineA graded change in a trait along a geographic axis Ex: lactate dehydrogenasefrequency is higher in cold water (allows faster swimming in fish) 25
    • 1.00.80.6 Mummichog0.40.2 0 46 44 42 40 38 36 34 32 30 Latitude (°N) (° Maine Georgia Cold (6°C) Warm (21°C) 26
    • Mutation A change in the nucleotidesequence of DNACauses new genes & alleles to arise Only mutations ingamete-producingcells can be passed to offspring 27
    • Point Mutation: a change in 1 base in a gene 28
    • Effects of PointMutations Mutations in noncodingregions of DNA are often harmless due to redundancy Mutations resulting in a change in protein production are often harmful Mutations may also be beneficial & increase an organism’s fit into its environment 29
    • Types of MutationsDeletions Disruptions Rearrangements Duplication More More More Less harmful harmful harmful harmful Genes can take on new functions 30
    • 31
    • Mutation Rates Low in animals & plants: avg 1 mutation in every 100,000 genes per generation Often higher in prokaryotes & viruses Prokaryotes & viruses have short generation times so mutations can quickly produce genetic variation 32
    • SexualReproduction Shuffles existing alleles into new combinations Recombination More important than mutation in producing genetic differences …Why? 33
    • FlowerSymmetryinAntirrhinumSpecies 34
    • Recombination During Meiosis 35
    • Gene Pool: all the alleles for all loci in a population 36
    • Porcupine herd MAP AREA Beaufort Sea Porcupine herd range overlap Fortymile herd rangeFortymile herd 37
    • Calculate the Frequency of an Allele in a Population:Total # of alleles at a locus = total # of individuals x 2 38
    • Total # of Dominant orRecessive Alleles at a Locus 2 alleles for each 1 allele for each homozygous heterozygousdominant or recessive individual individual plus… 39
    • If there are 2 alleles at a locus, p & q are used to represent their frequenciesThe frequency of all alleles in a population will add up to 1 p+q=1 p q 40
    • Hardy- Hardy-WeinbergPrincipleDescribes a hypothetical population that is not evolving In real populations, allele & genotype frequencies change over time If a population does not meet H-W criteria, then the population is evolving 41
    • Hardy- Hardy- WeinbergEquilibrium Allele & genotype frequencies in a population remain constant from generation to generation In a population where gametes randomly contribute to the next generation, allele frequencies will not change Mendelian inheritance preserves genetic variation in a population 42
    • CRCRCWCWCRCW 43
    • Selecting Alleles at Random from a Gene Pool randomFrequencies of alleles Gametes producedp = frequency of Each EachCR allele = 0.8 egg: sperm:q = frequency ofCW allele = 0.2 80% 20% 80% 20% chance chance chance chance Alleles in the equilibrium population 44
    • If p & q represent the relative frequencies of the only two possible alleles in a population at a particular locus, then:p2 & q2 are the frequencies of the homozygous genotypes 2pq is the frequency of the heterozygous genotype 45
    • Parent 80% CR (p = 0.8) 20% CW (q = 0.2)Generation: Sperm CR CW (80%) (20%) F1: 64% (p2) 16% (pq) CRCR CRCW 16% (qp) 4% (q2) CRCW CW CW 46
    • F1: 64% CRCR, 32% CRCW, and 4% CWCW Gametes of this generation: 64% CR + 16% CR = 80% CR = 0.8 = p 4% CW + 16% CW = 20% CW = 0.2 = q Genotypes in the next generation:F2: 64% CRCR, 32% CRCW, and 4% CWCW plants With random mating, these gametes will result in the same mix of genotypes 47
    • The 5 H-W conditions for nonevolving populations are rarely met in nature: Random No mutations mating Extremely No natural large selection population size No gene flow 48
    • 3 Major Factors of Evolutionary Change Natural Genetic Gene FlowSelection Drift 49
    • NaturalSelection Differential reproductive success Results in certain alleles beingpassed to the next generation in greater proportions than other alleles 50
    • Genetic Drift Allele frequencies can fluctuateunpredictably from one generation to the next Reduces geneticvariation through loss of alleles The smaller asample, the greater the chance of deviation from a predicted result 51
    • 52
    • 53
    • CR CR CR CR CW CW CR CR CR CR CR CW CR CW CR CR CR CR CW CW CR CR CR CR CW CW CR CR CR CR CR CW CR CW CR CR CR CR CR CR CR CW CW CW CR CR CR CR CR CR CR CW CR CW CR CW CR CR CR CR Generation 1 Generation 2 Generation 3p (frequency of CR) = 0.7 p = 0.5 p = 1.0q (frequency of CW ) = 0.3 q = 0.5 q = 0.0 54
    • Founder Effect Occurs when a few individuals become isolated from a larger population Allele frequencies in thesmall founder population may differ from those in the larger parent population Ex: Amish 55
    • Polydactyly 56
    • Bottleneck Effect Occurs when population size is reduced due to a sudden change in the environment The resulting gene pool may no longer reflect the original population’s gene pool If the population remains small, it may be further affected by genetic drift57
    • Original Bottlenecking Survivingpopulation event population 58
    • Genetic Drift & the GreaterPrairie Chicken Habitat loss caused a severe reduction in the population of greater prairie chickens in Illinois The surviving birds had low levels of genetic variation Only 50% of their eggs hatched 59
    • Pre-bottleneck Post-bottleneck (Illinois, 1820) (Illinois, 1993)Rangeof greaterprairiechicken 60
    • Greater Prairie ChickenResearch, cont. DNA from museum specimens used to compare genetic variation before & after bottleneck Results showed a loss of alleles at several loci Introduced prairie chickens from other states to increase gene pool diversity Successfully introduced new alleles & increased egg hatch rate to 90% 61
    • Number % Population Location of alleles of eggs size per locus hatchedIllinois 1930–1960s 1,000–25,000 5.2 93 1993 <50 3.7 <50Kansas, 1998 750,000 5.8 99(no bottleneck)Nebraska, 1998 75,000– 5.8 96(no bottleneck) 200,000Minnesota, 1998 4,000 5.3 85(no bottleneck) 62
    • Effects of Genetic Drift Significant in small populations Causes allele frequencies to change at random Can lead to a loss of genetic variation within populations May cause harmful alleles to become fixed 63
    • Gene Flow Movement of alleles among populations Transferred through movement of fertile individuals or gametes Usually reduces differences between populations over time More likely than mutation to directly alter allele frequencies 64
    • 65
    • 66
    • Gene Flow & Decreasing Fitness Ex: Bent grass Alleles for copper tolerance are beneficial in populations near copper mines, but harmful to those in other soils Windblown pollen moves alleles between populations Movement of unfavorable alleles into a population decreases the fitness between organism & environment 67
    • 70 NON- MINE NON-Index of copper tolerance MINE SOIL MINE 60 SOIL SOIL 50 Prevailing wind direction 40 30 20 10 0 20 0 20 0 20 40 60 80 100 120 140 160 Distance from mine edge (meters) 68
    • Population in which the 60 surviving females Central eventually bred population 50 Central NORTH SEA EasternSurvival rate (%) Eastern population Vlieland, 40 the Netherlands 2 km 30 20 10 0 Females born Females born in central in eastern Parus major population population 69
    • Gene Flow & Increasing Fitness Ex: Insecticideresistance in mosquitoes Insecticides have been used to kill mosquitoes that carry West Nile virus & malariaAlleles have evolved in some mosquitopopulations that confer insecticide resistance The flow of theseresistance alleles into apopulation can increase its fitness 70
    • 71
    • 72
    • 73
    • Why are the phrases“survival of the fittest” and“struggle for existence” misleading? 74
    • RelativeFitnessReproductive success isgenerally more subtle & depends on many factors The contribution anindividual makes to the gene pool of the next generation… …relative to the contributions of other individuals 75
    • 76
    • 3 Types of SelectionDirectional Disruptive Stabilizing 77
    • Directional Selection Original population Phenotypes (fur color) Evolved population Favors individuals at78 one extreme of the phenotypic range
    • 79
    • Disruptive Selection Original population Phenotypes (fur color) Evolved population Favors individuals at80 both extremes of the phenotypic range
    • 81
    • Stabilizing Selection Original population Phenotypes (fur color) Evolved population Favors intermediate variants82 & acts against extreme phenotypes
    • 83
    • NaturalSelection & Adaptive Evolution Natural selection increases the frequencies of alleles that enhance survival & reproduction Adaptive evolution occurs as the match between an organism & its environment increases Because the environment can change, adaptive evolution is a continuous dynamic process 84
    • 85
    • Bones shown in green are movable. LigamentMovable jawbones in snakes 86
    • SexualSelection Natural selection for mating success May result in sexual dimorphism Can lead to significant differences between secondary sexual traits 87
    • 88
    • 89
    • 90
    • Types of Sexual Selection IntersexualIntrasexual selection selection (Mate choice) 91
    • Intrasexual Selection Competition between individuals of one92 sex (often males) for mates of the opposite sex
    • 93
    • Intersexual Selection (Mate Choice) Sooty Grouse mating ritual Occurs when individuals of one sex (usually94 females) are more choosy in selecting their mates
    • Male showiness can increasehis chances of attracting a female, butalso decrease his overall chances of survival 95
    • Good GenesHypothesis One explanation for the evolution of female preference If a trait is related to male health, selection should favor both the male trait & the female preference for that trait Ex: Gray tree frog mating call 96
    • Significance ofCall Duration on Mate Choice Long-Calling (LC) & Short-Calling (SC) Does call duration indicate the male’s overall genetic quality? Do females choose mates based upon this trait? 97
    • EXPERIMENT Female gray tree frog SC male LC male SC sperm  Eggs  LC sperm Offspring of Offspring of SC father LC father Fitness of these half-sibling offspring compared 98
    • RESULTSOffspring Performance 1995 1996Larval survival LC better NSDLarval growth NSD LC betterTime to metamorphosis LC better LC better (shorter) (shorter)NSD = no significant difference; LC better = offspring of LC males superior tooffspring of SC males. 99
    • The Preservation of Genetic Variation Balancing Diploidy selection Frequency- Heterozygote dependent advantage selection Neutral variation 100
    • Diploidy Maintains genetic variation in the form of hidden recessive alleles 101
    • Balancing Natural selection maintains stable frequencies of 2 or more phenotypicSelection forms in a population Biston betularia morpha typica Biston betularia morpha carbonaria 102
    • Heterozygote Advantage Heterozygotes have a higher fitness than both homozygotes Natural selection will tend to maintain 2 or more alleles at that locus The sickle-cell allele causes mutations in hemoglobin, but also provides malaria resistance 103
    • Key Frequencies of the sickle-cell allele 0–2.5% 2.5–5.0%Distribution of 5.0–7.5%malaria caused by 7.5–10.0%Plasmodium falciparum(a parasitic unicellular eukaryote) 10.0–12.5% >12.5% 104
    • Frequency-Frequency-Dependent Selection “Left-mouthed” P. microlepis The fitness of a phenotype decreases if it becomes too common in the 1.0 “left-mouthed” individuals “Right-mouthed” population P. microlepis Frequency of Selection can favor the least common phenotype 0.5 in a population Ex: scale-eating fish 0 (Perissodus) 1981’82 ’83 ’84 ’85 ’86 ’87 ’88 ’89 ’90 Sample year 105
    • NeutralVariation Genetic variation that appears to provide no selective advantage or disadvantageEx: Variations in noncoding regions of DNA Ex: Variations in proteins that have little effect on function or reproductive fitness 106
    • Why Natural Selection Cannot Fashion “Perfect” Organisms Selection can act Evolution is limited only on existing by historical variations constraints Chance, natural Adaptations are selection, & theoften compromises environment interact 107
    • 108
    • Credits by Rob Swatski, 2013 Visit my website for more Anatomy study resources! http://robswatskibiology.wetpaint.com http://www.flickr.com/photos/rswatskiPlease send your comments and feedback to: rjswatsk@hacc.eduImages used in this work bear a This work bears an Creative Commons license and Attribution-Noncommercial are attributed to their original Share Alike Creative authors. Commons license. 109