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Biology (653)
BIO152H5 (140)
Chapter 26

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Fiona Rawle

Chapter 26 notesIf gene flow ends allele frequencies in isolated populations are free to diverge meaning that populations begin to evolve independently of each other For example when 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 move to the other populationIf mutation selection and genetic drift cause isolated populations to diverge sufficiently distinct types or species formthat is the process of speciation takes placeSpeciation is a splitting event that creates two or more distinct species from a single ancestral group When speciation compete a new branch has been added to tree of life Speciation results from genetic isolation and genetic divergenceGenetic isolation results from lack of gene flow and divergence occurs between selection genetic drift and mutation proceed independently in the isolated populationsSpecies an evolutionarily independent population or group of populationsFour criteria for identifying species1Biological species concept2Morphospecies concept3Ecological species concept4Phylogenetic species conceptAccording to biological species concept critical criterion for identifying species is reproductive isolation This is a logical yardstick because no gene flow occurs between populations that are reproductively isolated from each other Distinct species if two different populations do not interbreed in nature or fail to produce viable offspring and fertile offspringReproductive isolation stop gene flow between populations1Prezygotic isolation prevents individuals of different species from mating2Postzygotic isolation the offspring of matings between members of different species do not survive or reproduceTABLE 261 PAGE 504 Biological species concept has disadvantages The criterion of reproductive isolation cannot be evaluated in fossils or in species that reproduce asexually Also its difficult to apply when closely related populations do not happen to overlap with each other geographically
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