Biology

• Variation


  Differences between individuals of the same species
• Types of variation


  • Continuous
  • Discontinuous
• Continuous variation


  • Examples: height, weight, IQ
  • Has intermediate values
  • Caused by both gene and environment
  • Results in a range of phenotypes
• Discontinuous variation


  • Examples: blood group, fingerprint, seed of peas & seed color of peas
  • No intermediate values
  • Caused by gene
  • Results in a limited number of phenotypes
• Phenotype


  Physical characteristic of a human
• Types of mutation


  • Gene mutation - random change in DNA base sequence
  • Chromosome mutation - change in chromosome number
• Gene mutation


  Cannot be changed, can pass to next generation. Example: cancer
• Chromosome mutation


  Will not be passed to next generation. Example: Down's Syndrome
• If a disease name contains 'Syndrome', it is caused by chromosome mutation
• Importance of mutation


  • Genetic variation, new alleles formed
  • Example: virus
• Substances that can cause mutation

  • Ionising radiation (gamma rays, X-rays, UV)
  • Chemicals (smoking, asbestos, pesticides)
• Mutation can cause cancer in humans
• Sources of genetic variation in populations

  • Mutations
  • Meiosis
  • Random mating
  • Random fertilization
• Adaptive features


  Inherited features/characteristics that help an organism survive and reproduce in its environment
• Fitness


  Probability of an organism surviving and reproducing in its environment
• Hydrophytes (water plants)


  • Large air spaces in leaves to float and absorb sunlight
  • Stomata mainly on upper epidermis for gas exchange
  • Small roots to easily extract nutrients from water
• Xerophytes (desert plants)


  • Thick waxy cuticles to minimize water loss
  • Small needle-shaped leaves to reduce surface area
  • Extensive shallow roots for quick water absorption
• Random mutations in bacteria


  Cause genetic variation and antibiotic resistance, which increases in frequency in the population
• Artificial selection


  Selective breeding by humans
• Artificial selection process


  1. Select individuals with desirable features

  2. Cross these individuals

  3. Select offspring with desirable features

  4. Repeat for many generations
• Uses of artificial selection

  • Improve crop plants
  • Improve domesticated animals