chapter24 - BIOL 1020 CHAPTER 24 LECTURE NOTES Chapter 24:...

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BIOL 1020 – CHAPTER 24 LECTURE NOTES Chapter 24: The Origin of Species (Macroevolution) I. Macroevolution is essentially the formation of new species ( speciation ) and accompanying events A. species: “Kind of living thing”; the word “species” is both plural and singular B. relatively easy to define for sexual organisms, hard for asexual organisms and extinct species 1. biological species concept (for sexual organisms) a species is one or more populations whose members are capable of interbreeding and producing fertile offspring, and whose members are reproductively isolated from other such groups not always clear-cut, because some can interbreed under “artificial” conditions but don’t appear to do so in nature sometimes, “race” and “subspecies” designations are used, but often different specific epithets are used when there are clear morphological differences involved 2. asexual species – definition based on biochemical (think DNA sequence) and morphological differences; no solid rules also includes use of “race,” “subspecies,” and “strain” designations in asexual species, microevolution over time directly leads to macroevolution (speciation) 3. phylogenetic species concept or evolutionary species concept a species is a single line of descent (lineage with a unique genetic history) that maintains its distinctive identity from other lineages this is a more comprehensive concepts (it works for both sexual and asexual species) but, it can be hard to clearly define and agree upon “distinctive identity” C. the basis of macroevolution in sexual species is microevolution coupled with reproductive isolation II. Reproductive isolation can occur in a variety of ways A. reproductive isolation is any means of preventing gene flow between two species; for a new species to evolve from an existing (sexually reproducing) species, there must be a reproductive isolating mechanism in place B. reproductive isolating mechanisms can be classified as either prezygotic or postzygotic 1. prezygotic barriers – prevent fertilization (zygote formation) between gametes from two species habitat isolation (or ecological isolation) – isolation by differences in habitat occupied at the time of mating; examples: some garter snakes; some flycatchers temporal isolation – isolation by differences in timing of mating; examples: mating seasons in some skunks; flowering time in some plants; mating time in some fruit flies behavioral isolation
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This note was uploaded on 12/05/2011 for the course BIOL 1020 taught by Professor Dute during the Fall '06 term at Auburn University.

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chapter24 - BIOL 1020 CHAPTER 24 LECTURE NOTES Chapter 24:...

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