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