test 2. - Chapter 24 The Origin of Species Charles Darwin...

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Chapter 24 The Origin of Species Charles Darwin (1859) The origin of species, by means of natural selection. 1. Evolution occurs in population 2. Natural selection is the mechanism. Species Biological Species Concept A population whose members can potentially interbreed in nature to produce viable ( fertile) offspring. Reproductive Barriers isolate populations from one and other. Reproductive Barriers A complete barrier would result in no gene flow An incomplete barrier could still reduce gene flow. Pre-zygotic vs. Post-zygotic Pre-zygotic barriers impede mating or hinder fertilization if mating does occur. Post-zygotic barriers prevent a hybrid zygote from developing into a viable, fertile adult. Pre-zygotic: Habitat Isolation 1. Geographic Isolations 2. Ecological Isolations 3. Behavioral (Mate Choice) Isolations 4. Temporal Isolations 5. Mechanical Isolations 6. Gametic Isolations Post-zygotic 1. Reduced hybrid viability 2. Reduced hybrid fertility- hybrid sterility ( in the extreme) 3. Hybrid Breakdown (Reduced viability or fertility occurs in the offspring of hybrids) Speciation The process by which new species form. 2 Requirements: 1. Reproductive Isolation of population- gene flow sufficiently reduced. 2. Genetic Divergence ( divergent evolution) 2 main modes: Allopathic vs. sympatric Allopathic- divergence occurs in geographic isolation Sympatric- divergence occurs despite lack of geographic isolation. Allopathic Vs. Sympatric
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Sympatric Speciation- divergence occurs lack of geographic isolation. Polyploids: organisms with extra sets of chromosomes; can result in sympatric speciation in one generation. The origin of a polyploidy individuals is usually a mistake in meiosis or mitosis. Autopolyploidy vs. Allopolyploidy Autopolyploid is an individual that has > two chromosomes sets all from a single species. Allopolyploid is an individual > two chromosome sets, derived from different species. From Micro to Marco Evolution Micro Evolution- evolutionary change below the species level; change in allele frequencies in a population over generation. Macro Evolution- Speciation and all broader scale evolutionary patterns and processes. Anagenesis- sufficient micro-evolutionary changes may occur that the earlier population is considered a separate species from the later population. Cladogenesis- branching evolution occurs as speciation events accumulates.
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The formation of each new branch is a macro evolutionary Broad pattern across the results threes are… Adaptive Radiation One species gives rise to many others in geologically short period of time. (e.g. Darwin’s Finches) Islands are a good place to find adaptive Radiation Many opportunities for genetic divergence by natural selection (E.g. Hawaiian Silverswords) Tempo of Evolution 1. Gradualism 2. Punctuated Equilibrium Evolutionary Novelties - Evolutionary novelties usually arise as modification of existing traits. Evolutionary Development
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This note was uploaded on 06/13/2011 for the course SOCL 2001 taught by Professor Mecom during the Spring '07 term at LSU.

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test 2. - Chapter 24 The Origin of Species Charles Darwin...

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