Investigating Selection

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  • Investigating Selection
    • Antibiotic resistance
      • Directional selection- individuals with alleles for characteristics of extreme type more likely to survive and reproduce
      • Could be response to environmental change
      • Bacteria involving antibiotic resistance example of DS
      • 1) Some individuals in population have allele that gives them resistance to antibiotics
      • 2) Population exposed to antibiotic, killing bacteria without resistant allele
      • 3) Resistant bacteria survive and reproduce without competition, passing allele for antibiotic resistance to offspring
      • 4) After time, most organisms in population will carry antibiotic resistance gene
    • Human Birth Weight
      • Stabilising selection- individuals with alleles towards middle of range more likely to survive and reproduce
      • Occurs when environment isnt changing, reduces range of possible characterisitics
      • Example of stabilising selection is human birth weight
      • 1) Humans have range of birth weights
      • 2) Very small babies less likely to survive- find it hard to maintain body temperature
      • 3) Giving birth to large babies difficult, they are less likely to survive too
      • 4) Conditions most favourable to medium sized babies- weight of human babies tends to shift towards middle of range
    • Interpreting data
      • Describe what data shows- quote graph
      • Suggest cause
    • Aseptic Technique
      • Used to prevent contamination of cultures by unwanted organisms
      • Contamination can affect growth of microorganism being investigated
      • Disease causing microbes may also make you ill
      • Regularly disinfect work surfaces to minimise contamination
      • Work near bunsen flame. Hot air rises, microbes drawn away from culture
      • Sterilise wire inoculation loop before and after each use by passing through hot bunsen flame for 5 seconds
      • Briefly flame neck of glass container of broth just after opening and just before closing-prevents unwanted organisms falling in
      • Sterilise all glass ware before and after use e.g. in autoclave


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