MECHANISMS OF EVOLUTION. POPULATIONS, NOT INDIVIDUALS, EVOLVE An organism cannot change its...
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Transcript of MECHANISMS OF EVOLUTION. POPULATIONS, NOT INDIVIDUALS, EVOLVE An organism cannot change its...
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MECHANISMS OF EVOLUTION
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POPULATIONS, NOT INDIVIDUALS, EVOLVE
An organism cannot change its phenotype. A phenotype can become more predominant in a population, though.
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Gene PoolAll the alleles of the population’s genes.
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ALLELIC FREQUENCY
The percentage of any specific allele in the gene pool.
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GENETIC EQUILIBRIUM
A population in which the allele frequencies remain the same over many generations.
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CHANGES IN GENETIC EQUILIBRIUM
A population in genetic equilibrium is not evolving.
When equilibrium of the gene pool is disrupted, evolution occurs.
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Changes in equilibrium may be the result of mutations.
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Gene FlowOrganisms moving in (immigration) or out (emigration) of a population creates changes in the allelic frequencies of the gene pool.
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Hardy-Weinberg Principle
• In order for genetic equilibrium to remain, these conditions must be met:–No mutations
–No immigration or emigration
–Random mating
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GENETIC DRIFT
The alteration of allelic frequencies by chance events.
Can greatly affect small populations.
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NATURAL SELECTION ACTS ON VARIATIONS
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THE EVOLUTION OF SPECIES
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SPECIATION
• Occurs when members of similar populations no longer interbreed to produce fertile offspring within their natural environment.
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PHYSICAL BARRIERS CAN PREVENT INTERBREEDING
-Geographic isolation
-Reproductive isolation
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CHANGE IN CHROMOSOME NUMBER
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SPECIATION CAN OCCUR QUICKLY OR SLOWLY
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GRADUALISM
• The idea that species originate through a gradual change of adaptations. Example: horses in fossil record.
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PUNCTUATED EQUILIBRIUM
• The idea that speciation occurs in rapid bursts with long periods of genetic equilibrium between.
• Caused by abrupt temperature changes or introduction of a competitive species.
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PATTERNS OF EVOLUTION
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ADAPTIVE RADIATION
• Many species evolve from a single species.
• Example – Darwin’s finches and Hawaiian Island honeycreepers.
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DIVERGENT EVOLUTION
• Two or more species with the same common ancestor become different species due to isolation.
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CONVERGENT EVOLUTION
• Two species with different ancestors evolve similar traits due to selective pressures in the environment.
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