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Patterns and Processes of Evolution
Macroevolutionary Patterns Large-scale (more than a single species) Occurs over long periods of time
Microevolution Small-scale (within a single species) Forms variations in populations
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Speciation – Isolating MechanismSpecies – group of organisms that interbreed to
produce fertile offspring under normal conditions –
share a common gene poolSpeciation – formation of a new species
Requires reproductive isolation – organisms do not interbreed; gene pools become separateBehavioralGeographicTemporal
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Patterns of Extinction
Background Extinction – “business as usual” extinction – slow and steady
Mass Extinction – many species become extinct over a short period of timeCauses:AsteroidVolcanic eruptionsMoving continentsChanging sea levels
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Rates of Evolution
Gradualism – change in species is slow and steady
Punctuated Equilibrium – long periods of stability followed by short periods of rapid change
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Patterns of Macroevolution:
Adaptive RadiationA single species evolves into many speciesOften occurs when a niche opens up
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Organisms come to resemble one another but evolved differently
Source of analogous structures!
Examples: Dolphins and sharks Marsupials and
mammals
Patterns of Macroevolution:
Convergent Evolution
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Coevolution
Organisms with close ecological relationships evolve togetherPollinators and flowers
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The Role of Genes in Evolution
In terms of genetics, evolution is the change in the frequency of alleles in a population’s gene pool
Natural selection leads to that change
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Genetic DriftRandom change in allele frequency –
changes in the gene pool of a small population due to chance
Types of Genetic Drift: Bottleneck Effect – change in allele
frequency following dramatic reduction in population size
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Genetic Drift Founder Effect – small group colonizes a
new habitat
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Molecular Evolution
Molecular Clocks – use mutation rates in DNA to estimate time two species have been evolving independently
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Molecular Evolution: Hox Genes
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Genes which control an organism’s basic body plan Anterior/posterior ends Limbs, wings
small sequence changes during embryological development can cause large changes in adults