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Three Requirements for Natural Selection

Genetic Basis for Phenotypes. Three Requirements for Natural Selection. Phenotypic Variation. Fitness Differential based on Phenotypes. Mechanisms of Reproductive Isolation. Pre-Zygotic – prevent fertilization from ever occurring 1. Temporal – different breeding seasons (frogs)

Jeffrey
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Three Requirements for Natural Selection

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  1. Genetic Basis for Phenotypes Three Requirements for Natural Selection Phenotypic Variation Fitness Differential based on Phenotypes

  2. Mechanisms of Reproductive Isolation Pre-Zygotic – prevent fertilization from ever occurring 1. Temporal – different breeding seasons (frogs) 2. Habitat – different areas (meadows vs. stream side) 3. Behavioral – different courtship (bowerbirds) 4. Mechanical – different reproductive structures (flowers) 5. Gametic – different sperm-egg binding sites

  3. Mechanisms of Reproductive Isolation Post-Zygotic – prevent functioning adulthood 1. Hybrid Inviability – arrested development 2. Hybrid Sterility – adult not able to reproduce 3. Hybrid Breakdown – F2 sterility

  4. How to get from molecular data to a tree • Align sequences for all species to compare & identify differences between species 2. Generate a distance matrix 3. Choose the two species with the least differences and group them 4. Re-draw your distance matrix with those species clustered as one group 5. Continue process of grouping until all accounted for 6. Draw tree

  5. .5 + .5 = 1 (x-0.5) + (x-1) = 12 2x – 1.5 = 12 2x = 13.5 x = 6.75 human chimpanzee Rhesus m. horse donkey platypus 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Cytochrome c amino acid substitutions

  6. Radiation of mammals Vertebrates evolve Fish vs. Reptiles Reptiles vs. Birds Reptiles vs. Mammals Separation of plants & animals

  7. 5’ 3’ exon intron leader & trailer flanking regions

  8. Calculating Rates of Molecular Evolution # of nucleotide changes/site/year # of nucleotide differences in DNA region of interest counted for species of interest growth hormone gene between rats and mice = 1800 differences divide by total number of nucleotides in DNA region to get #changes/site if there are 15000 nucleotides in GH gene: 1800/15000 = 0.12 divide by number of years since species had a common ancestor (identified from fossil record) 0.12/15,000,000 = 8 x 10-9 changes/site/year *more changes occur than we can presently see (e.g., forward & reverse mutations; additions + deletions) – models used to predict actual number of changes *once you get a few points for the graph, if the rate is stable you can predict evolutionary divergence times by knowing the rate, how many differences, and how big the gene is

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