Evolution and Natural Selection

• Natural Selection

  • From Darwin's 4 major observations;
  • All organisms potentially could over reproduce
  • Pop numbers tend to remain constant over time
  • Organisms demonstrate variation - individuals in species differ from each other
  • Some inherited variation - offspring resemble parents genes/alleles inherited
  • Pop size limits: selection pressures
  • Predation
  • Intraspecific competition
  • Finite resources
  • Disease
  • Climate, temp or pH variation
  • Human influence
  • Genetic variation
  • Crossing over
  • Independent assortment
  • Random mutations
  • Random fertilisation
  • Variation give individuals advantagagrous alleles
  • Pop compete to survive + breed
  • Advntaged better at get resources + have more offspring
  • Pass alleles onto; next gen has higher proportion of it
• Antibiotic Resistance

  • Antibiotics chemicals made naturally by few bacteria + fungi, kill competing microbes
  • Stop bacterial cells multiplying + correctly forming cell walls
  • Since weakened blebbing occur
  • Can be phagocytosed
  • Strong selection pressure; overuse lead to antibiotic resistance
  • Some bacteria produce enzymes to break down antibiotics
  • Result of plasmid DNA mutation
  • Overuse + incorrect use led to resistant strains
  • We should always finish prescribed course
  • Only take antibiotics if a bacterial infection + absolutely necessary
  • Antibiotic multi discs used in hospitals to identify effective antibiotics
  • Cheap, quick + efficient
  • Enables early treatment
  • Leads to correct antibiotic use; reduce resistance
• Pesticide Resistance

  • Some insects are pest, eat food crops or cause crop damage; some carry diseases
  • Humans use pesticide chemicals to kill them; strong selection pressures
  • If any insect, by mutation, develops resistance, it survives to breed + pass on resistant genes to next gen
  • Rapid reproduction + large insects numbers lead to rapid resistance spread
  • Problems of Pesticide Resistance
  • Crop yields + quality decrease
  • Diseases like malaria
  • Farmers inc dose
  • Many insecticides used are biodegradable; persist in insects consumed by predators
  • Insecticides accumulate in food chains causing toxicity to top carnivores inc humans
  • Called bioaccumulation or biomagnification