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  • 1. CHAPTER 24 LECTURE SLIDES Prepared by Brenda Leady University of ToledoTo run the animations you must be inSlideshow View. Use the buttons on theanimation to play, pause, and turn audio/texton or off. Please note: once you have usedany of the animation functions (such as Play orPause), you must first click in the whitebackground before you advance the next slide. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  • 2. Genetic drift Changes allelic frequency due to random chance Random events unrelated to fitness Favors either loss or fixation of an allele  Frequency reaches 0% or 100% Faster in smaller populations 2
  • 3. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1.0 N = 10 All BB 0.75Frequency of B allele N = 1,000 0.5 N = 10 0.25 0.0 0 10 20 30 40 50 All bb Generations 3
  • 4. Bottleneck Population reduced dramatically and then rebuilds Randomly eliminated members without regard to genotype Surviving members may have allele frequencies different from original population Allele frequencies can drift substantially when population is small New population likely to have less genetic variation 4
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  • 6. Founder effect Small group of individuals separates from a larger population and establishes a new colony Relatively small founding population expected to have less genetic variation than original population Allele frequencies in founding population may differ markedly from original population 6
  • 7. Please note that due to differingoperating systems, some animationswill not appear until the presentation isviewed in Presentation Mode (SlideShow view). You may see blank slidesin the “Normal” or “Slide Sorter” views.All animations will appear after viewingin Presentation Mode and playing eachanimation. Most animations will requirethe latest version of the Flash Player,which is available athttp://get.adobe.com/flashplayer. 7
  • 8. Neutral theory of evolution Non-Darwinian evolution Neutral variation  Much of the variation seen in natural populations is caused by genetic drift  Does not preferentially select for any particular allele Most genetic variation is due to the accumulation of neutral mutations that have attained high frequencies due to genetic drift Neutral mutations do not affect the phenotype so they are not acted upon by natural selection 8
  • 9.  Main idea is that much of the modern variation in gene sequences is explained by neutral variation rather than adaptive variation Sequencing data supports this idea Nucleotide substitutions much more likely in 3rd base of codon (usually doesn’t change amino acid) than 1st or 2nd (usually does change amino acid) Changing the amino acid is usually harmful to the coded protein 9
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