11-Macro Evolution

11-Macro Evolution - Macroevolution Macroevolution :...

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Macroevolution Macroevolution - Ideas about how species arise and diversify - Main tenet of evolution: species arise from preexisting species - Patterns of species distributions in time and space - Speciation     : appearance of a new species - Extinctions     : complete disappearance of species Definition of species - Once seemed simple…now less clear - Must account for: - Distinctiveness of species at location - Connection of different populations of a species - Biological Species concept:     - One or more population(s) of individuals interbreed under natural   conditions  to produce fertile offspring Criteria for species - Interbreeding must produce fertile offspring - Horse X donkey   mule (infertile) Horse and donkey are from different species - Can interbreed under natural conditions but don’t have fertile offspring so  different species - Interbreeding must occur under natural circumstances : - Dog X coyote   coydog - Fertile, but does not occur naturally  - 2 nd  and 3 rd  generations infertile and subject to disease at a young age - No species concept is perfect. - A lot of variation in the “domestic” dog. Don’t know if they can interbreed The beginning of species: speciation - Gene flow maintains similarities among populations of a species - For speciation to occur gene flow must be blocked - No gene flow   divergence   reproductive isolation - Modes of reproductive isolation:
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- Prezygotic        Before fertilization - Postzygotic        After fertilization Reproductive isolation Barriers to reproduction Species A Pre-zygotic    post-zygotic Mating   Fertilization   Offspring Species B Mating: habitat, behavioral isolation Fertilization: mechanical, gametic isolation - Preventing interbreeding b/c of shape, … Offspring: Hybrid breakdown, reduced hybrid viability (inability of hybrids to maintain  healthy lifestyles and to grow to sexual maturity), sterility Table 22.1: Reproductive Isolating Mechanisms The geography of speciation - Speciation occurs readily in the absence of gene flow - Allopatric      speciation - Geographic barrier separates populations - Squirrels on each side of the Grand Canyon, physically separated - Don’t interbreed, have achieved reproductive isolation
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This note was uploaded on 03/25/2010 for the course BIO 11000 taught by Professor Friedman during the Spring '10 term at Purdue.

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11-Macro Evolution - Macroevolution Macroevolution :...

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