BIO120H1 Lecture Notes - Lecture 9: Erythranthe Lewisii, Erythranthe Cardinalis, Sympatric Speciation

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14 Oct 2018
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BIO120H1 Full Course Notes
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BIO120H1 Full Course Notes
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Two distinct species are reproductively isolated from one another: they constitute distinct gene pools that don"t intermingle. Even if two species live close together and their hybrids are fertile, as long as there are reproductive barriers that prevent regular interbreeding, they are distinct species. Isolated populations diverge, and when that divergence has gone on for a sufficiently long time, reproductive barriers develop as a by-product of evolution. A species is a reproductive and evolutionary community; it is the unit of evolution, the thing that evolves. Species don"t arise for the purpose of filling up empty niches in nature. Allopatric speciation, the most common form of speciation, occurs when populations of a species become geographically isolated. When populations become separated, gene flow between them become limited or completely ceases. Over time, selection and genetic drift will act differently on these two different genetic backgrounds, creating genetic differences between the two new species: sympatric speciation.

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