Three requirements for natural selection
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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)

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Three Requirements for Natural Selection

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Genetic Basis for Phenotypes

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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.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


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Radiation of mammals

Vertebrates evolve

Fish vs. Reptiles

Reptiles vs. Birds

Reptiles vs. Mammals

Separation of plants & animals


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5’

3’

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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