01:119:115 Lecture 20: Biology- Lecture 20 (The Evolution of Populations Microevolution - Chapter 23.1 - 23.4)

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Evolution = change in populations over generations not changes in individuals over their lifetime individuals do not evolve. Natural selection acts on individuals but only populations evolve. Microevolution = minor evolutionary changes of populations over a few generations = change in allele frequencies in population over generations. Genetic variations are necessary for evolution to occur. Phenotype = product of inherited genotype + environmental influences. Only genetically determined part of phenotype variation can affect evolution. Natural selection can only act on variation with a genetic component. Genetically determined phenotypic variation: some phenotypic are either-or basis . Either have the trait or not. Example: mendel"s pea plant characters: other phenotypic vary in gradation. Vary along a continuum within a population. Determined by 2 or more genes. Example: height in humans: source of genetic variation. Three mechanism cause allele frequency change: natural selection, genetic drift, gene flow. Genetic variation among individuals in genes or nucleotide sequences.

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