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

Updated May 2006Created by C. Ippolito May 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

Updated May 2006Created by C. Ippolito May 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

Updated May 2006Created by C. Ippolito May 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

Updated May 2006Created by C. Ippolito May 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

Updated May 2006Created by C. Ippolito May 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

Updated May 2006Created by C. Ippolito May 2006 Allele Frequencies Allele Frequency –percentage of the population carrying a particular allele Hardy-Weinberg Principle –represented by math equations p 2 + 2pq + q 2 = 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

Updated May 2006Created by C. Ippolito May 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 –p 2 = homozygous dominant in population –2pq = heterozygous in population –q 2 = homozygous recessive in population

Updated May 2006Created by C. Ippolito May 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

Updated May 2006Created by C. Ippolito May 2006 Speciation evolution of a new species through time Original PopulationStep 1 – Original Population –interbreeding population sympatric - all allele together BarrierStep 2 – Barrier (usually geographic isolation) –populations separated by a barrier allopatric – alleles divided between two groups gene flow stopped Different Environmental PressuresStep 3 – Different Environmental Pressures –each population experiences different selective pressures –gene pools change Barrier RemovedStep 4 – Barrier 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

Updated May 2006Created by C. Ippolito May 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