Three Requirements for Natural Selection

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Three Requirements for Natural Selection
Phenotypic Variation
Fitness Differential based on Phenotypes
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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
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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
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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
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(x-0.5) (x-1) 12 2x 1.5 12 2x 13.5 x
6.75
human
chimpanzee
Rhesus m.
horse
donkey
platypus
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Cytochrome c amino acid substitutions
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Radiation of mammals
Vertebrates evolve
Fish vs. Reptiles
Reptiles vs. Mammals
Reptiles vs. Birds
Separation of plants animals
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exon
intron
leader trailer
flanking regions
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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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