BIO152H5 Chapter Notes - Chapter 26: Dusky Seaside Sparrow, Species Problem, Genetic Drift

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Speciation occurs when populations of the same species become genetically isolated by lack of gene flow and then diverge from each other due to selection, genetic drift, or mutation. If gene flow between populations stops, then mutation, selection, and drift begin to act on the populations independently. If a new mutation creates an allele that changes the phenotype of individuals in one population, there is no longer any way for that allele to appear in the other population. As a result, allele frequencies and other characteristics in the populations diverge. When allele frequencies change sufficiently over time, populations become distinct species. Species: evolutionarily independent population or group of populations. 3 different sets of criteria to identify them: the biological species concept. The critical criterion for identifying species is reproductive isolation. This is a logical measuring stick because no gene flow occurs between populations that are reproductively isolated from each other. Prezygotic isolation: prevents individuals of different species from mating.

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