4.4 Genetic diversity and adaptation

• What is genetic diversity?

  Number of different alleles of genes in a population
• What are alleles and how do they arise?

  ● Variations of a particular gene (same locus) → different DNA base sequence

  ● Arise by mutation
• What is a population?

  A group of interbreeding individuals of the same species.
• Explain the importance of genetic diversity

  • ● Enables natural selection to occur
  • ● As in certain environments, a new allele of a gene might benefit its possessor
  • ● By resulting in a change in the polypeptide (protein) coded for that positively changes its properties
  • ● Giving possessor a selective advantage (increased chances of survival and reproductive success)
• What is evolution?

  • ● Change in allele frequency (how common an allele is) over many generations in a population
  • ● Occurring through the process of natural selection

  Adaptation and selection are major factors in evolution and contribute to the diversity of living organisms.
• Explain the principles of natural selection in the evolution of populations

  1. Mutation = Random gene mutations can result in [named] new alleles of a gene
  2. Advantage = In certain [named] environments, the new allele might benefit its possessor [explain why] → organism has a selective advantage
  3. Reproductive = success Possessors are more likely to survive and have increased reproductive success
  4. Inheritance = Advantageous allele is inherited by members of the next generation (offspring)
  5. Allele frequency = Over many generations, [named] allele increases in frequency in the population
• Describe 3 types of adaptations

  • ● Anatomical - structural / physical features that increase chance of survival
  • ● Physiological - processes / chemical reactions that increase chance of survival
  • ● Behavioural - ways in which an organism acts that increase chance of survival
• Explain directional selection, with examples


  Example:

  • Antibiotic resistance in bacteria

  Key feature - who has a selective advantage?:

  • Organisms with an extreme variation of a trait eg. bacteria with high level of resistance to a particular antibiotic

  Change in environment:

  • Yes, usually eg. antibiotic introduced

  Effect on population over many generations:

  • Increased frequency of organisms with / alleles for extreme trait
  • Normal distribution curve shifts towards extreme trait

  
• Explain stabilising selection, with examples

  Example:

  • Human birth weight

  Key feature - who has a selective advantage?:

  • Organisms with an average / modal variation of a trait eg. babies with an average weight

  Change in environment?

  • No, usually stable

  Effect on population over many generations:

  • Increased frequency of organisms with / alleles for average trait
  • Normal distribution curve similar, less variation around the mean

  
• RP6: Explain examples of aseptic techniques that could be used

  ● Wash hands with soap / disinfect surfaces → kill microbes / prevent contamination

  ● Sterilise pipette / spreader / boil agar growth medium → kill microbes / prevent contamination

  ● Flame neck of bottle of bacteria → kill microbes / prevent contamination

  ● Bunsen burner close → upward current of air draws air-borne microbes away to prevent contamination

  ● Lift lid of petri dish slightly / minimise opening → prevent entry of microbes / contamination
• RP6: Describe a method to investigate the effect of antimicrobial substances (eg. antibiotics, disinfectants, antiseptics) on microbial growth - steps 1-3 up to bacteria on agar

  1. Prepare area using aseptic techniques (as above)
  2. Use a sterile pipette to transfer bacteria from broth to agar plate using aseptic techniques (as above)
  3. Use a sterile spreader to evenly spread bacteria over agar plate

  
• RP6: Describe a method to investigate the effect of antimicrobial substances (eg. antibiotics, disinfectants, antiseptics) on microbial growth - steps 4-6 from bacteria on agar

  1. 4. Use sterile forceps to place same size discs that have been soaked in different types / concentrations of antimicrobials for same length of time, onto agar plate (at equal distances)
  2. 5. Lightly tape lid onto plate (not fully sealed), invert and incubate at 25°C for 48 hours
  3. 6. Measure diameter of inhibition zone around each disc and calculate area using πr^2

  
• RP6: Why is it important to maintain a pure culture of bacteria?

  ● Bacteria may outcompete bacteria being investigated

  ● Or could be harmful to humans / pathogenic
• RP6: Why hold lid with 2 pieces of tape instead of sealing it completely?

  • ● Allows oxygen in preventing growth of anaerobic bacteria
  • ● Which are more likely to be pathogenic / harmful to humans
• RP6: Why use a paper disc with water / no antimicrobial agent?

  ● Act as a control

  ● Ensuring antimicrobial prevented growth, not paper disc
• RP6: Why incubate upside down?

  Condensation drips onto lid rather than surface of agar
• RP6: What if inhibition zones are irregular?

  Repeat readings in different positions, calculate a mean
• RP6: Why not use higher antimicrobial conc.?

  More bacteria killed so clear zones may overlap
• RP6: Why incubate at 25°C or less?


  Below human body temp to prevent growth of pathogens
• RP6: Describe how data about the effect of antimicrobial substances can be presented as a graph

  • ● Categorical data → bar chart (X axis type of antimicrobial, Y axis area of zone of inhibition / $mm^3$)
  • ● Continuous data → line graph joined by a line of best fit (X axis concentration of antibiotic / $μgmL^-1$, Y axis area of zone of inhibition / $mm^3$)
• RP6: Explain the presence and absence of clear zones

  1. Clear zones → antimicrobial diffuses out of disc into agar, killing / inhibiting growth of bacteria
  2. ● Larger clear zones → more bacteria killed → more effective antimicrobial
  3. No clear zones → if antibiotic used, bacteria may be resistant or antibiotic may not be effective against that specific bacteria