Chapter 25 2.02.08

Chapter 25 2.02.08 - Honors Biology Book Notes Chapter 25...

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Honors Biology Book Notes Chapter 25 – Speciation 2/02/08 - Speciation o When gene flow ends, allele frequencies in isolated population diverge and populations begin to evolve independently of each other o Speciation : process is usually a splitting event that creates two or more distinct species from a single ancestral group resulting from genetic isolation (lack of gene flow) and genetic divergence (selection, genetic drift, mutation) o Species : an evolutionarily independent population/group of populations o 3 Criteria for identifying a species (1) Biological species concept (2) Morphospecies concept (3) Phylogenetic species concept o Biological Species Concept Biological species concept: says that critical criterion for identifying species is reproductive isolation [in other words, if species do not interbreed in nature or do not produce offspring when they do, then they are considered distinct species] Reproductively isolated populations are evolutionarily independent Reproductive isolation results from (1) Prezygotic isolation : prevents individuals of different species from mating [occurs before mating can occur] (2) Postzygotic isolation : offspring of matings between members of different species do not survive or reproduce Flaw in BSC – does not apply to fossils or species that reproduce asexually, or populations that do not overlap geographically but are similar o Morphospecies Concept Morphospecies concept : researchers identify evolutionarily independent lineages by differences in size, shape, or other morphological features Distinguishing features are most likely to arise if populations are independent and isolated from gene flow
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