updated may 2006created by c. ippolito may 2006 chapter 16 origin of new species pages 359-377
TRANSCRIPT
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Updated May 2006 Created by C. IppolitoMay 2006
Chapter 16Origin of New Species
Pages 359-377
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Updated May 2006 Created by C. IppolitoMay 2006
Evidence for Evolution• Galapagos Islands
– Finches adapted to different roles• Six species feed on ground• Six species feed in trees• One species feeds in bushes
– All use a different food source– Niches – “profession” of an organism in its particular
environment
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Updated May 2006 Created by C. IppolitoMay 2006
Selection• Artificial Selection
– Breeders choose “variations” – Determine “breeding” stock based on these
• Natural Selection– After his voyage, proposed that nature could do
the same
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Updated May 2006 Created by C. IppolitoMay 2006
Population and Ecological Evidence• Industrial Melanism
– E.B. Ford – observed natural selection of the pepper moth
• Before Industrial Revolution most moths were white
– Forests were covered with white lichen on tree bark
• After Industrial Revolution most moths were dark
– Forest covered with soot favored darker moths
– University of Michigan – mouse experiment
• Similar result with owl and white and dark mice against different background
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Updated May 2006 Created by C. IppolitoMay 2006
Genetic and Molecular Evidence
• Genetics was unknown to Darwin– could not explain where “variations” originated
• Modern Genetics– Variations come from
• Mutations in DNA• Recombination during meiosis
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Updated May 2006 Created by C. IppolitoMay 2006
Population Genetics• Population
– group of one species living in a specific area
• Gene pool– all of the genes of a population of organisms– more different genes in gene pool the better the
chances of survival– if the frequency of genes in the pool changes
evolution occurs
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Updated May 2006 Created by C. IppolitoMay 2006
Allele Frequencies• Allele Frequency
– percentage of the population carrying a particular allele
• Hardy-Weinberg Principle– represented by math equations
• p2 + 2pq + q2 = 1 and (p + q)2 =1• p = dominant allele q = recessive allele
– allele frequencies remain constant if:• nonrandom mating – no preferences in choosing mates• no mutations – changes in alleles• no migration – no one leaves or enters the pool• no selection – no alleles favored in survival• population is large – no genetic drift
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Updated May 2006 Created by C. IppolitoMay 2006
Example of Hardy Weinberg• p = frequency of dominant gene• q = frequency of recessive gene
– (p + q)2 = 1 if we take square root of both sides– p + q = 1
• if we “expand” the binomial equation– p2 = homozygous dominant in population– 2pq = heterozygous in population– q2 = homozygous recessive in population
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Updated May 2006 Created by C. IppolitoMay 2006
Microevolution v. Macroevolution• MicroevolutionMicroevolution
– changes that occur within populations and species– caused by
• variation• natural selection• genetic drift• speciation
• MacroevolutionMacroevolution– changes above the species level
• evolutionary trends• mass extinction
– inferred from • data of microevolution• fossil record
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Updated May 2006 Created by C. IppolitoMay 2006
Speciation• evolution of a new species through time• Step 1 – Original PopulationOriginal Population
– interbreeding population • sympatric - all allele together
• Step 2 – Barrier Barrier (usually geographic isolation)– populations separated by a barrier
• allopatric – alleles divided between two groups• gene flow stopped
• Step 3 – Different Environmental PressuresDifferent Environmental Pressures– each population experiences different selective pressures– gene pools change
• Step 4 – Barrier RemovedBarrier Removed– populations so different cannot mate!!! new species
• Seasonal IsolationSeasonal Isolation – now mate at different times
• Mechanical IsolationMechanical Isolation – physical differences prevent mating
• Reproductive IsolationReproductive Isolation – gametes no longer compatible/ zygote stops developing
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Updated May 2006 Created by C. IppolitoMay 2006
Evolutionary Mechanisms• GradualismGradualism
– slow gradual change of gene pools over time
• Punctuated EquilibriumPunctuated Equilibrium– long stable periods of little change– followed by short, rapid bursts of significant change