1323441488_CHAPTER_16_SPR - EVOLUTION/LECTURE1 Evolution...

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EVOLUTION/LECTURE1 file:///E|/CH16-SPECIATION-SPRING-2008/CHAPTER%2016_SPR_2008.HTML[12/8/2011 2:57:06 PM] Evolution ( PCB 4674 ). Chapter 16. Mechanisms of speciation Main topics of lecture: I: Species concepts: 1.- What is a species? 2.- Biological species concept 3.- The phylogenetic species concept 4.- The morphospecies concept 5.- Applying species concept II: Mechanisms of isolation: 6.- Physical isolation 7.- Changes in chromosomes as a barrier to gene flow III: Mechanisms of divergence: 8.- Genetic drift 9.- Natural selection 10.- Sexual selection IV: Secondary contact: 11.- Reinforcement of parental forms 12.- Hybridization, creation of new species, and hybrid zones V: The genetics of differentiation and isolation: 13.- Classical genetics 14.- Analyzing quantitative trait loci I: Species concepts: 1.- What is a species? 1.1.- In previous chapters we investigated how mutation, natural selection, migration and drift act to change allele frequencies within populations; now we ask how these four forces can lead to genetic differences between populations. In addition for providing foundation for studying the history of life, studying speciation has important practical applications.
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EVOLUTION/LECTURE1 file:///E|/CH16-SPECIATION-SPRING-2008/CHAPTER%2016_SPR_2008.HTML[12/8/2011 2:57:06 PM] Much of the material we explore is fundamental to establish effective strategies for preserving biodiversity, and to managing genetically engineered organisms that are released into the environment. To begin our analysis we start with the most fundamental question: What is a species? 1.2.- All human cultures recognize different types of organisms in nature and name them. People intuitively group like with like. The challenge to biologists has been to move beyond these informal judgments to a definition of species that is mechanistic and testable, and to a classification system that accurately reflects the evolutionary history of organisms 1.3.- This has been difficult to do. In the past 30 years alone there have been at least half a dozen species concepts proposed. There has been even philosophical debates about whether the unit we call species actually exists in nature or whether it is merely a linguistic and cultural construct 1.4.- However, all these definitions agree that species share a distinguishing characteristics, which is EVOLUTIONARY INDEPENDENCE . Evolutionary Independence occurs when mutation, selection, migration, and drift operate on each species separately. This means that species form a boundary for the spread of alleles. Consequently, different species follow independent evolutionary trajectories. The differences among species concepts center on the problem of establishing practical criteria for identifying evolutionary independence 2.- Biological species concept 2.1.- Under the biological species concept (BSC), the criterion for identifying evolutionary independence is reproductive isolation. The BSC has been the textbook definition of a species since Ernst Mayr proposed in 1942. The definition of a species
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1323441488_CHAPTER_16_SPR - EVOLUTION/LECTURE1 Evolution...

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