BIOLOGY (variation and evolution)

• Antibiotic resistance bacteria


  • Pesticide resistance
  • Warfarin resistance rats
• Antibiotic resistance


  1. Genetic variation exists due to spontaneous mutations

  2. Mutation may give bacterium antibiotic resistance

  3. If antibiotic is administered the bacterium is better adapted and survives

  4. Bacterium reproduces passing on its resistance variant

  5. Frequency of antibiotic resistance allele increases
• Over prescription and antibiotic misuse leads to increased antibiotic resistance
• Cystic Fibrosis


  Recessive condition resulting in production of sticky mucus affecting lungs and digestive system
• Cystic Fibrosis genotypes


  • FF-healthy phenotype
  • Ff-healthy phenotype, carrier of disease
  • ff- cystic fibrosis phenotype
• Modelling natural selection


  1. Use different coloured squared paper to camouflage

  2. Large piece of blue paper

  3. Equal no of blue and white small pieces of paper on background (represent prey)

  4. Volunteer collects as many squares as possible

  5. Record no. of blue and white squares remaining, repeat 3 times

  6. Expected there's more blue left than white
• Limitations of the model: Squares don't move, extreme difference in square colours, paper is 1 colour, potential bias by volunteer, not affected by other factors
• Limitations of the model compared to reality: Prey move, prey more similar in colour, environment not 1 colour, no bias, other factors affect survival
• Evolution


  Gradual change in inherited traits within a population over time, occurs due to natural selection
• Natural selection


  Organisms with more useful adaptations, better suited for survival, they can breed and pass on this useful gene to future generations, less useful characteristics are lost
• Antibiotic resistance amongst bacteria is developing quickly
• The organisms with the most useful adaptations survive. These organisms breed and pass on their genes for useful adaptations, to the next generation. The next generation is better adapted for survival. This is natural selection (Survival of the fittest). Wallace and Darwin proposed this theory.
• Continuous variation


  Produces characteristics which do not fall into distinct categories e.g. height
• Discontinuous variation


  Produces characteristics which fall into distinct categories e.g. eye colour
• Extinction


  When all members of a species die, not adapted to the environment, not adapted rapidly enough to changing conditions, out-competed by better adapted species
• Types of variation


  • Genetic - Differences in the genotype of organisms of the same species due to the presence of different alleles, creating differences in phenotypes
  • Environmental - Differences in phenotype that are acquired during the lifetime of an organism due to environmental factors e.g. diet, lifestyle, climate
  • Combination of both genetic and environmental factors
• Genetic variation


  Due to sexual reproduction or spontaneous mutations
• Sexual reproduction


  Creates genetic variation in organisms, meiosis produces genetically different gametes so forms unique individuals
• Asexual reproduction


  Doesn't create genetic variation as mitosis is used so 2 identical daughter cells are created (clones)
• Spontaneous mutation


  Random change in the base sequence of DNA resulting in genetic variants, caused by chemicals and ionizing radiation, can be neutral, minor, or complete change in phenotype
• Gene therapy


  Techniques used to counteract the effects of a defective allele within DNA, either by insertion of a functional allele or turning off the faulty allele
• Ethical issues with gene therapy: expensive, religious objections to gene manipulation, health implications and side effects
• Human Genome Project

  • Science research project involving thousands of scientists across the globe
  • Successfully mapped the entire human genome
  • Enabled understanding of how lifestyle factors interact with genes
  • Identified disease causing alleles for better early treatment
  • Enabled prediction of individual response to certain drugs and development of new drugs
• theory of natural selection - the process by which organisms better adapted to their environment are more likely to survive, reproduce and pass on advantageous traits
• natural selection is driven by competition between individuals within populations for limited resources such as food or mates.
• individuals with characteristics that make them better suited to their environment will be more successful at competing for these resources than those without these adaptations.
• Artificial selection - selective breeding of plants and animals to produce desired characteristics
• mutation = random

  change to the base sequence in the DNA resulting in genetic variants
• why do mutation changes occur?

  due to chemicals + ionising radiation