Chapter 26 Speciation

Chapter 26 Speciation - Chapter 26: Speciation How are new...

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Unformatted text preview: Chapter 26: Speciation How are new species formed? Genetic isolation Genetic divergence 1 How are species defined? * (pp. 527530) Species are often thought of as evolutionary units Individuals within a species are evolving together Individuals of different species evolve independently (Fig. 26.1) Useful conceptually, but not practical There is no universal, practical definition of species Life is complex 1.1 Biological species Biological species are defined by reproductive isolation Different biological species either: Dont breed in nature Breed but fail to produce offspring Produce inviable offspring offspring do not develop to adult- hood Produce sterile offspring offspring that cannot themselves re- produce 1 Mechanisms of isolation Mechanisms of isolation are often divided into two classes: Prezygotic isolation refers to any mechanism that prevents suc- cessful mating Postzygotic isolation refers to any mechanism that prevents off- spring from producing offspring of their own Zygote means a cell formed by the fusion of a sperm and an egg Mechanism examples Pre- or post-? Different malaria parasites breed inside different hosts Different species of doves can nest together, but eggs fail to hatch or chicks fail to grow The offspring of horses and donkeys grow up to be healthy, infertile adults Sea urchin eggs cannot be penetrated by sperm from other species Species of pine trees release and receive pollen and different times of year Disadvantages of the biological species concept 2 1.2 Morphological species...
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This note was uploaded on 04/13/2011 for the course BIO 1M03 taught by Professor Jonathanstone,jamesquinn during the Spring '11 term at McMaster University.

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Chapter 26 Speciation - Chapter 26: Speciation How are new...

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