origins of life on earth 4.7-4.8 billion year history
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Origins of Life on Earth 4.7-4.8 Billion Year History. Evidence from chemical analysis and measurements of radioactive elements in primitive rocks and fossils. Life developed over two main phases: Chemical evolution (took about 1 billion years) - PowerPoint PPT PresentationTRANSCRIPT
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Origins of Life on Earth4.7-4.8 Billion Year History
• Evidence from chemical analysis and measurements of radioactive elements in primitive rocks and fossils.
• Life developed over two main phases:– Chemical evolution (took about 1 billion years)
• Organic molecules, proteins, polymers, and chemical reactions to form first “protocells”
– Biological evolution (3.7 billion years)• From single celled prokaryotic bacteria to eukaryotic creatures
to eukaryotic multicellular organisms (diversification of species)
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Summary of Evolution of Life
Formationof the
earth’searly
crust andatmosphere
Small organic
moleculesform inthe seas
Large organic
molecules(biopolymers)
form inthe seas
First protocells
form inthe seas
Single-cellprokaryotes
form inthe seas
Single-celleukaryotes
form inthe seas
Variety ofmulticellular
organismsform, firstin the seas and lateron land
Chemical Evolution(1 billion years)
Biological Evolution(3.7 billion years)
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DNA
Watson and Crick and their model of DNA
www.chem.ucsb.edu/~kalju/chem110L/public/tutorial/images/WatsonCrick.jpgen.wikipedia.org/wiki/DNA
DNA replication
• The double-helix structure of DNA was discovered in 1953.
• This showed how genetic information is transferred from one cell to another almost without error.
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MUTATIONS
• Changes in the structure of the DNA
• Adds genetic diversity to the population
• May or may not be adaptive– Depends on the environment!
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Mutation
Mutant fruitfly
• Mutations are rare and often have damaging effects. •Mutations may be caused by radiation, viruses, or carcinogens.
• However, occasional mutations or copying errors can and do occur when DNA is replicated.
•Consequently organisms have special enzymes whose job it is to repair faulty DNA.
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Rates of mutation
• Measured by phenotypic effects in humans:– Rate of 10-6 to 10-5 per gamete per generation
• Total number of genes?– Estimates range from about 30,000 to over
100,000!– Nearly everyone is a mutant!
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Rates of mutation
• Mutation rate of the HIV–AIDS virus:– One error every 104 to 105 base pairs
• Size of the HIV–AIDS genome:– About 104 to 105 base pairs
• So, about one mutation per replication!
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Rates of mutation
• Rates of mutation generally high• Leads to a high load of deleterious (harmful)
mutations
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Types of mutations
• Point mutations– Base-pair substitutions– Caused by chance errors during synthesis or repair
of DNA– Leads to new alleles (may or may not change
phenotypes)
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Types of mutations
• Gene duplication– Result of unequal crossing over during meiosis– Leads to redundant genes• Which may mutate freely• And may thus gain new functions
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Types of mutations
• Chromosome duplication– Caused by errors in meiosis (mitosis in plants)– Common in plants• Leads to polyploidy• Can lead to new species of plants
– Due to inability to interbreed
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Transitions are more common than transversions becauseDNA repair enzymes can recognize wrong insertion representing a a transition better than a transversion
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Variation
•Some mutations will persist and increase genetic variation within a population.
• Variants of a particular gene are known as alleles. For example, the one of the genes for hair colour comprises brown/blonde alleles.
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Natural Selection
en.wikipedia.org/wiki/Image:Mutation_and_selection_diagram.svg
• Mutant alleles spread through a population by sexual reproduction.
• If an allele exerts a harmful effect, it will reduce the ability of the individual to reproduce and the allele will probably be removed from the population.
• In contrast, mutants with favorable effects are preferentially passed on
Selection of dark gene
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When faced with a change in environmental condition, a population of a species can get MAD:
•MIGRATE to a more favorable location• ALREADY be adapted •DIE
Natural selection can only act on inherited alleles already present in the population.
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Reproductive capacity may limit a population’s ability to adapt
If you reproduce quickly (insects, bacteria) then your population can adapt to changes in a short time.
If you reproduce slowly (elephants, tigers, corals) then it takes thousands or millions of years to adapt through natural selection
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What’s Evolution?The change in a POPULATION’S genetic makeup (gene pool) over time (successive generations)
Those with selective advantages (i.e., adaptations), survive and reproduce.
All species descended from earlier ancestor species
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4 major mechanisms that drive evolution:
• Natural Selection• Mutation• Gene Flow• Genetic Drift
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Three types of Natural Selection• Directional
– Allele frequencies shift to favor individuals at one extreme of the normal range• Only one side of the distribution
reproduce• Population looks different over
time• Stabilizing
– Favors individuals with an average genetic makeup• Only the middle reproduce• Population looks more similar over
time (elim. extremes)• Disruptive (aka Diversifying)
– Environmental conditions favor individuals at both ends of the genetic spectrum • Population split into two groups
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Microevolution
Small genetic changes in a population such as the spread of a mutation or the change in the frequency of a single allele due to selection (changes to gene pool)
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Four Processes cause Microevolution
Mutation (random changes in DNA—ultimate source of new alleles)
Exposure to mutagens or random mistakes in copyingRandom/unpredictable relatively rare
Natural Selection (more fit = more offspring)Gene flow (movement of genes between pop’s)Genetic drift (change in gene pool due to random/chance events)
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Ex: Peppered Moth
http://en.wikipedia.org/wiki/Image:Biston.betularia.7200.jpgen.wikipedia.org/wiki/Image:Biston.betularia.f.carbonaria.7209.jpgen.wikipedia.org/wiki/J._B._S._Haldane
• The Peppered Moth is an example of Natural Selection in action discovered by Haldane
• During the Industrial Revolution the trees on which the moth rested became soot-covered.
• This selected against the allele for pale colour in the population (which were poorly camouflaged from predators) and selected for the dark colour allele.
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Microevolution
www.puppy-training-solutions.com/image-files/dog-breed-information.jpg
• The dog is another example of how selection can change the frequency of alleles in a population.
• Dogs have been artificially selected for certain characteristics for many years, and different breeds have different alleles. • All breeds of dog belong to the same species, Canis lupus (the wolf) so this is an example of Microevolution as no new species has resulted.
Dogs are wolves
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Macroevolution
Long term, large scale evolutionary changes through which new species are formed and others are lost through extinction.
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• Macroevolution is the cumulative result of a series of microevolutionary events– Typically seen in fossil record– Nobody around to see the small, gene pool
changes over time.
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Macroevolution
www.ingala.gov.ec/galapagosislands/images/stories/ingala_images/galapagos_take_a_tour/small_pics/galapagos_map_2.jpg
Galapagos finches
• However, if two populations of a species become isolated from one another for tens of thousands of years, genetic difference may become marked.
• If the two populations can no-longer interbreed, new species are born. This is called Macroevolution.
• Darwin’s Galapagos finches are an example of this process in action.
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COEVOLUTION: Interaction Biodiversity
• Species so tightly connected, that the evolutionary history of one affects the other and vice versa.