Genetics and Evolution

• Outline the theory of evolution by natural selection

  1. Individuals of a species show a wide range of variation for a characteristic

  2. Those with the characteristic most suited to the environment will survive breed most successfully

  3. The desirable characteristic that has enabled the individuals to survive are passed onto their offspring
• Why was Darwin's theory of evolution not accepted initially
• Creationism


  Most people believed in this
• Insufficient evidence to prove the theory
• The mechanism of variation and inheritance was not known at the time
• Lamarck's theory of inheritance


  That changes during the lifetime of an organism can be inherited
• Speciation


  The formation of a new species, when two populations become so varied that they cannot interbreed to produce fertile offspring
• Species


  A group of organisms with similar characteristics which are able to interbreed to produce fertile offspring
• Outline the process of speciation through geographic isolation


  1. Two populations of the same species are separated geographically

  2. Geographic isolation prevents interbreeding and mixing of genes between the populations

  3. Due to different selection pressures, different mutations occur producing different phenotypes in each population

  4. Over time, the two populations may evolve so that they are not able to interbreed
• Genetic variation


  Important in speciation as it produces phenotypic variation, some of which are better suited to the environment and are selected for
• How did Mendel study inheritance

  Through carry breeding experiments on plants and analysing the ratio of characteristics in offspring
• Why was Mendel's work not recognised until after his death
• He could not explain the mechanism of inheritance, as chromosomes were only discovered after his death
• It was not communicated well to other scientists and not published in a reputable scientific journal
• Evidence used to show evolution

  • Fossils
  • Antibiotic resistance in bacteria
• How are fossils formed

  1. Parts of organisms that have not decayed due to conditions needed for decay being absent

  2. Parts of organisms that have been replaced by minerals as they decayed eg. bones

  3. Traces of organisms are preserved, covered in sediment and becoming rock
• Why are there few traces of early life-forms left behind
• How fossils act as evidence for evolution

  Scientists can identify the ages of the fossils and use them to show how organisms change over time
• Evolutionary trees


  Branches indicate where speciation has occurred
• Extinction


  Where there are no individuals of a species still alive
• Factors that may lead to extinctions

  • New disease
  • Predation
  • Competition
  • Changes to the environment
  • Catastrophic events
• Why bacteria evolve quickly

  The fast rate of their reproduction
• Outline the process of antibiotic resistance bacteria evolving

  1. Mutations occur in bacteria producing genetic variation

  2. Certain strains are resistant to antibiotics and are not killed when the antibiotic is applied

  3. Resistant strains survive and reproduce

  4. Over time, the population of the resistant strains increase
• Why resistant strains of bacteria are dangerous

  People have no immunity to them and there is no effective treatment
• What can be done to reduce the rate of development of antibiotic resistant bacteria

  • Refrain from inappropriately prescribing antibiotics eg. for viral diseases
  • Patients should complete the prescribed course of antibiotics
  • Restrict agricultural uses of antibiotics
• Why is it difficult to keep up with emerging resistance strains