Variation

• Variation


  Interspecific variation

  • Differences between diff species
  • Used to classify diff species

  Intraspecific variation

  • Differences in same species
  • Natural selection basis
  • Influenced by either: Genetic or Environmental factors
  • GENETIC CAUSES
  • Allele differences
  • Sexual reproduction, from meiosis + random fertilisation
  • Mutations involve DNA replication errors, occurs sexually + asexually
  • Inherited
  • Darwin’s 3rd + 4th observations
  • Environmental Causes
  • Environmental effects on gene expression
  • Not caused by DNA differences; not inherited
  • Intraspecific variation divided to 2 types; Discontinuous + Continuous Variation

  Importance

  • Natural selection
  • Environmental selection pressures
  • Survivors breed + pass on desirable adaptive features
  • Selective Breeding
  • By humans since agriculture began
  • Humans select those with desired features
• Intraspecific Variation

  Discontinuous

  • Individuals in distinct groups/categories, no intermediates
  • Controlled by 1 or few genes → monogenic
  • Phenotype expression not usually affected by environment
  • Qualitative - diff between individuals unmeasurable
  • Represented graphically by a bar chart; examples:
  • ABO blood group
  • Tongue-rolling ability
  • Resistance to pesticides
  • Resistance to antibiotics

  Continuous

  • Individuals fall between 2 extremes, many intermediates
  • Controlled by 2+ genes; called polygenes/polygenic
  • Each gene give additive component to phenotype, expression strongly affected by environment
  • Quantitative - diff between individuals measured
  • Represented graphically by histogram, w/ large sample size
  • Normal Distribution Curve can be obtained; examples:
  • Height
  • Skin colour
  • Eye colour
  • Lef length
• Adaptations

  • Feature that enhances survival + long-term reproductive success
  • Help organisms cope w/ environmental stress; selection pressures
  • Find food + water
  • Defend from predators
  • Survive physical conditions - temp changes
  • Respond to environmental changes
  • Reproduce successfully
  • Separate 3 adaptations diff categories
  • Behavioural
  • E.g. Survival or Courtship
  • Combination of innate + learned behaviour
  • Anatomical
  • E.g. Body covering, Colour, Teeth + Mimicry
  • Physiological
  • Processes inside organism
  • E.g. Hibernation, Antibiotic/Venom production + Changing metabolic reactions
  • Cactus are xerophytes
  • Accordion folded stem, can tighten into ridges in dry periods
  • Stem expands + rounds when water available