Updated May 2006Created by C. Ippolito May 2006 Chapter 16 Origin of New Species Pages 359-377.

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Updated May 2006 Created by C. IppolitoMay 2006

Chapter 16Origin of New Species

Pages 359-377

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

Selection• Artificial Selection

– Breeders choose “variations” – Determine “breeding” stock based on these

• Natural Selection– After his voyage, proposed that nature could do

the same

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

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

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

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

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

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

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

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

Updated May 2006Created by C. Ippolito May 2006 Chapter 16 Origin of New Species Pages 359-377.

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