Chapter 24 - Chapter 24: The Origin of Species Speciation:...

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Chapter 24: The Origin of Species Speciation: the process by which one species splits into two or more species Responsible for the diversity of life, yielding new species that differ from existing ones When one species splits, the species that result share many characteristics because they are descended from this common ancestral species (e.g., DNA) Microevolution: changes in allele frequencies in a population Macroevolution: the broad pattern of evolution over long time spans 24.1 The biological species concept emphasizes reproductive isolation Biological species concept: a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring—but do not produce viable, fertile offspring with members of other such groups The members of a biological species are united by being reproductively compatible Gene flow (the transfer of alleles between populations) holds the gene pool of a species together, causing its members to resemble each other more than they resemble other species Gene flow has the potential to hold the gene pool of a species together, so long as it is not outweighed by effects of selection or drift (either of which can result in populations diverging) Reproductive isolation: the existence of biological factors (barriers) that impede members of two species from producing viable, fertile offspring Such barriers block gene flow between the species and limit the formation of hybrids, offspring that result from an interspecific mating A single barrier may not prevent all gene flow but a combination of several barriers can effectively isolate a species’ gene pool Prezygotic barriers: block fertilization from occurring (most common in closely related species, act in one of three ways: 1. by impeding members of different species from attempting to mate 2. by preventing an attempted mating from being completed successfully 3. or by hindering fertilization if mating is completed successfully Postzygotic barriers:
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Chapter 24 - Chapter 24: The Origin of Species Speciation:...

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