Biology 1202

Biology 1202 - Biology 1202 3/25/2010 12:28:00 AM Chapter...

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Unformatted text preview: Biology 1202 3/25/2010 12:28:00 AM Chapter 24: The Origin of Species Concept 24.1 : The biological species concept emphasizes reproductive isolation Species: Latin for kind or appearance Which pair is two different species? o Two similar looking dragonflies ** o Two different looking dogs ( same species ) The Biological Species Concept o Defines a species as a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring. o Cannot be applied to Asexual organisms Fossils Organisms about which little is know regarding their reproduction Speciation (Figure 24.14) o Dependent on: Reproductive isolation Genetic drift, natural selection, etc., happening independently in two different populations which lead to genetic divergence The existence of biological factors that impede members of two species from producing viable, fertile offspring. Prezygotic barriers o Prevents eggs and sperm from coming together o Impede mating between species or hinder the fertilization of ova if members of different species attempt to mate. o (Figure 24.4) o Habitat isolation o Temporal isolation o Behavioral isolation o Mechanical isolation o Gametic isolation Post zygotic barriers o After fertilization o Often prevents the hybrid zygote from developing into a viable, fertile adult o Reduced hybrid viability Offspring dont develop into adulthood and successful mating o Reduced hybrid fertility- donkey crossed with a horse and the mule offspring is incapable of forming gametes o Hybrid breakdown the hybrid of two rice plants is weak and doesnt survive over many generations Genetic divergence Genomes of populations become incapable of interbreeding Establishing Reproductive Isolation (Figure 24.7) Two species of pine are found in the same habitat but release pollen at different times during the year. This is an example of o Temporal Isolation Concept 24.2: speciation can take place with or without geographic separation Speciation can occur in two basic ways o Allopatric speciation isolated geographically Other country Gene flow is interrupted or reduced when a population is divided into two or more geographically isolated subpopulations 1. Original population- single species; homogeneous habitat 2. Geographical isolation geographic barrier isolates populations 3. Genetic divergence- genetic drift, mutation, and natural selection cause genetic divergence 4. Barrier removed populations mix but dont interbreed o Sympatric speciation occupy the same area but become isolated...
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Biology 1202 - Biology 1202 3/25/2010 12:28:00 AM Chapter...

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