Chapter 15
Tracing Evolutionary History
1. Abiotic Synthesis of Small Organic Molecules (SOM)
2. Polymerization of SOM to form proteins and nucleic acids
3. Packaging of molecules and polymers into « protocells »
4. Self-replication of molecules necessary for « inheritance »
How Did Life Arise?
Early Earth Conditions
2. Early photosynthetic Bacteria forming Stromatoliths
1. Reducing atmosphere including water vapour, CO2, CH4, NH3, H2, H2S2, Nitrogen & its sulfids
The Miller Experiment
Mixture of gases simulating atmospheres of early Earth
Spark simulating lightning storms
Condensation chamber
Cold water cools chamber, causing droplets to form
Water vapor
Liquid containing amino acids and other organic compounds
1
2
3
4
Miller’s Experiment Revisited
Analysis of a 4.5 BY-old meteorite that landed in Australia in 1968 contains 80 types of amino acids, lipids, simple surgars and uracil
Alternate Theory for the Appearance of Amino Acids
Formation of ProtocellsMembrane-enclosed
vesicles form when lipids are mixed with water
Adding clay increase rate of vesicle formation while organic molecules concentrate on the surface of the clay
RNA monomers form short RNA polymersAssembly of complementary RNA chain, may
have been the first step in the replication of the original « gene »?
RNA formed the first genes?
Endosymbiosis
Learn.Genetics –U of Utah
Major Advances in Life History
Tree of Life
Use the ages of rocks to identify the ages of fossils found in them
Use radiometric dating
Carbon-14 for young fossils (½ life of 5730 years)
Potassium-40 for older fossils (½ life of 1.3 BY)
How do we know?
Geological Record
Plate Tectonics which caused continental drift causes allopatric speciation
Mass Extinctions wiped out many species at a time which allowed survivors to thrive with less competition/predation
Adaptive Radiation – usually following mass extinctions
« Evo-devo » – slight genetic changes can cause drastic morphological differences b/w species
Mechanisms of Macroevolution
Earth’s Tectonic Plates
Continental DriftSpecies became
separated as the continents drifted, then evolved separately
Lungfish Distribution
Mass Extinctions
Adaptive Radiation of Mammals after the Cretaceous Mass Extinction
Changes in Rate and Timing
Changes in Spactial Pattern
New Genes and Changes in Genes
Changes in Gene Regulation
EVO-DEVO (interface b/w evolutionary biology and developmental biology)
Paedomorphosis – adults that present some juvenille characteristic of an ancestral species
Example : This sexually mature Axoloti is a salamander that retained external gills instead of developing lungs in adulthood
Changes in Rate and Timing
Genes for prognathism are turned off early in humans, while the brain continues to develop at a faster rate after birth
Changes in Rate and Timing cont...
Changes in homeotic genes (HOX genes) or in how or where they are expressed changes body form
Changes in Spatial Pattern
Duplications of HOX genes and subsequent mutations allow for novel characteristics
Two duplications of the hox gene clusters seem to have occured in during the evolution of invertebrates to vertebrates allowing for backbones, jaws and limbs.
New Genes and Changes in Genes
Changes in Gene Regulation
Thought to be only one origin of light-sensitive cells shared among all animals with the capacity to detect light
Evolution of the Eye
A particular structure can become adapted for alternative functions
Feathers were probably used for mating rituals or thermoregulation in dinosaurs, but eventually became adapted for flight
Exaptation
Evolutionary trends depend on the interaction of the organism and their current environment
If the environment changes, the trend can change or even reverse
For example, without grasslands, there would not be a strong selection for grazers in horse ancestors
Evolution may not be GOAL-directed
Taxonomy
Phylogenic Trees (Cladograms)
Reading Phylogenic Trees
Creating Phylogenic Trees
Phylogentic Tree of LIFE!
Based on:
Shared characteristics
Molecular similarities (DNA or A.A. sequences)
Parsimony (simplest explanation is ususally the best)
Phylogenic Trees are Hypotheses
Genes that seem to have reliable rate of change over time can be used as molecular clocks
Molecular clocks help track evolutionary time
Commonly Used Molecular Clocks
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