3.4.4

• Genetic diversity

  The number of different alleles in a population

  enabling natural selection to occur
• What does genetic diversity enable

  Natural selection
• Allele frequencry

  The proportion of organism within a population carting a particular allele
• Four causes of genetic diversity

  1. Mutations
  2. Meiosis ( crossing over, independent segregation )
  3. Random fusion of gamete’s
  4. Environmental factors
• Selective advantage

  Increases chance of survival and reproductive success
• Evolution

  A change in the allele frequency over many generations in a population occurring through the process of natural selection or even by genetic drift ( founder effect or genetic bottleneck)
• Genetic drift

  Process where allele becomes more frequent in a small population due to random chance
• acronym for five marker for natural selection

  1. Mutation
  2. Adaptation
  3. Reproductive success
  4. Inheritance
  5. Allele frequency
• Explain natural selection. In the evolution of population

  1. Random gene mutations cause genetic diversity / variation as new alleles formed
  2. In certain environment the new alleles advantageous to its possessor (explain why ) so the organism has a selective advantage
  3. New allele provides a reproductive selective advantage So individual with this allele is more like to survive and reproduce
  4. advantageous allele inherited by members of the next generation
  5. Over many generations the frequency of advantageous allele in the population increases
• Three types of adaptation

  1. Anatomical
  2. Physiological
  3. Behavioural
• Anatomical adaptation

  Structural and physical features like fur
• Physiological adaptation

  Processes / chemical reactions (affinity of hb )
• Behavioural adaptation

  Ways in which an organic acts ( whales singing )
• Purpose of adaptation

  Increases survival chance
• Three types of selection

  1. Directional
  2. Stabilising
  3. Distruptive
• Directional selection

  1. Acts against one extreme
  2. The organism with the extreme variation of a trait have the selective advantage
  3. Occurs when theirs environmental change
  4. Modal trait changes
• Direct selection example

  Antibiotics

  • There is a mutation in a bacterial cell in a colony.
  • This could result in a bacterial cell with an allele for resistance for a particular antibiotic.
  • When this antibiotic is used, the resistant bacterial cell would survive and reproduce by binary fission.
  • All offspring would inherit the allele for resistance and the frequency of the allele increases.
  • This process would continue until the whole bacterial population are resistant to the antibiotic.

  
• Stabilising selection

  1. Acts against both extremes in a phenotype
  2. Organisms modal variation of a trait has the selective advantage
  3. Doesn’t require change in environment to occur and is usually stable
  4. Mode stays the same and the range decreases so there’s less variation around the mean
• Example of stabilising selection

  Human birth weight
• • Three factors reducing genetic diversity

  1. The founder effect
  2. Genetic bottlenecks
  3. Inbreeding