7_Macroevolution 9_10_2009

7_Macroevolution 9_10_2009 - Macroevolution* (Ch. 24.3 and...

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1 Macroevolution* (Ch. 24.3 and parts of other sections) *evolutionary change at or above the species level Many can accept microevolution but not macroevolution (e.g. Michael Behe, The Edge of Evolution, 2007) 2 From Speciation to Macroevolution • Macroevolution is the cumulative effect of many speciation and extinction events 3 The Modern Synthesis • Established in the 1930s and 1940s • Connected the units of evolution (genes) with the mechanism of evolution (selection on populations) • Integrated Darwinian evolution with Mendelian genetics + 4 Architects of the modern synthesis JBS Haldane G Ledyard Stebbins Theodosius Dobzhansky Sewall Wright (no need to memorize these guys)
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5 Natural selection is the primary mechanism of adaptive evolution • Natural selection accumulates and maintains favorable genotypes in a population • Depends on existence of heritable, genetic variation 6 Populations evolve, individuals do not In case you didn’t get that Populations evolve, individuals do not 7 Evolutionary Processes • Mutation and sexual recombination produce new variation • Selection, drift and gene flow alter a population’s genetic composition 8 Mutations • The raw material of evolution • A “two edged sword” - most mutations are deleterious but a few are beneficial and these provide the basis for evolutionary change A partial list of kinds of mutations • Point mutations • Insertions / Deletions • Gene duplications • Chromosome inversions • Polyploidization
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9 Single mutations rarely produce significant adaptive change. Most mutations are neutral or deleterious. 10 Mutation is a weak evolutionary force • The rate of mutation ( µ ) per gene, per generation varies from about 3x10 -9 to 7x10 -4 (that’s 0.000000003 - 0.0007) • From one generation to the next, max p = p 0 (1 - ), so change in p is negligible ( e.g. p 0 (1-0.0007) = 0.9993) • Over 100 generations, gene frequency would change from p 0 to p 0 e - t = 0.9324 11 However mutation + selection over time is powerful E. coli experiments show massive response to selection in replicate lines 12 Evolutionary Processes Mutation and sexual recombination produce new variation • Selection, drift and gene flow alter a population’s genetic composition
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13 Modes of Selection 14 Trait feature Directional selection Ex 1) Effects of the industrial revolution Ex 2) giraffe neck example 15 2. Stabilizing selection Selection against extremes birth weight 16 3. Disruptive selection Sneaker male Female Large male
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17 • Sexual selection is natural selection for mating success • Can result in sexual dimorphism • Sexually selected traits may be bad for survival Sexual Selection 18 19 Irish Elk RIP ~5700 BC (Too sexy for his own good?) When sexual selection goes amuck… 20 • Random assortment of chromosomes – With 46 pairs of chromosomes, humans can produce >8 million combinations of intact chromosomes • Crossing over of chromosomes adds a staggering possibility of additional variability How does sexual recombination create variation?
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This note was uploaded on 02/23/2010 for the course BISC 120Lg taught by Professor 11:00-01:50pm during the Fall '06 term at USC.

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7_Macroevolution 9_10_2009 - Macroevolution* (Ch. 24.3 and...

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