key concept a population shares a common gene pool
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KEY CONCEPT A population shares a common gene pool.
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Genetic variation in a population increases the chance that some
individuals will survive.• Genetic variation leads to phenotypic variation.• Phenotypic variation is necessary for natural selection.• Genetic variation is stored in a population’s gene pool.
– made up of all alleles in a population– allele combinations form when organisms have offspring
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• Allele frequencies measure genetic variation.– measures how common allele is in population
– can be calculated for each allele in gene pool
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Genetic variation comes from several sources.
• Mutation is a random change in the DNA of a gene.
• Recombination forms new combinations of alleles.
– can form new allele
– can be passed on to offspring if in reproductive cells
– usually occurs during meiosis
– parents’ alleles arranged in new ways in gametes
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Genetic variation comes from several sources.
• Hybridization is the crossing of two different species.– occurs when individuals can’t find mate of own species– topic of current scientific research
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Natural selection acts on distributions of traits.
• A normal distribution graphs as a bell-shaped curve.
• Traits not undergoing natural selection have a normal distribution.
– highest frequency near mean value
– frequencies decrease toward each extreme value
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Natural selection can change the distribution of a trait in one of three
ways. • Microevolution is evolution within a population.
– observable change in the allele frequencies – can result from natural selection
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• Natural selection can take one of three paths. – Directional selection favors phenotypes at one extreme.
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– Stabilizing selection favors the intermediate phenotype.
• Natural selection can take one of three paths.
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• Natural selection can take one of three paths. – Disruptive selection favors both extreme
phenotypes.