1.7 Evolution

• Define the term 'Evolution'

  The changes in organisms over generations as a result of genomic variations arising through mutation.
• Describe the 2 aspects to natural selection.

  • Non-random Increase in the frequency of DNA sequences that increase survival.
  • non-random reduction in the frequency of deleterious sequences.
• What are the changes in phenotype frequency the result of ?

  -Stabilising selection

  -Directional selection

  -Disruptive selection
• Describe stabilising selection.

  An average phenotype is selected for and extremes of the phenotype range are selected against.

  -e.g human birth weight, tree height
• Describe directional selection.

  One extreme of the phenotype is range is selected for and the average and other extreme is selected against.

  -e.g peppered moth, giraffe neck
• Describe disruptive selection.


  Two or more phenotypes are selected for.

  -e.g Galapagos finches, male chimpanzee mass
• Describe the process of vertical gene transfer.

  Genes are transferred from parent to offspring as a result of sexual or asexual reproduction.
• Describe the process of horizontal gene transfer.

  Genes are transferred between individuals in the same generation. This is often done by transferring plasmids.
• Why is natural selection rapid in prokaryotes?

  Short generation time.

  Horizontal gene transfer only occurs in prokaryotes. Vertical can occur in all.
• Describe the term 'species'

  A group of organisms capable of interbreeding to produce fertile offspring. These groups of organisms do not normally breed with other groups.
• Describe the importance of isolation barriers in speciation.


  This prevents Interbreeding and gene flow during speciation.
• State what speciation is and it's three steps.

  The generation of a new biological species by evolution as a result of a 3 step process:

  1. Isolation
  2. Mutation
  3. Selection
• State the two types of speciation.

  Geographical barriers lead to allopatric speciation. e.g rivers, mountains.

  Behavioural barriers lead so sympatric speciation. e.g breeding season.
• What evidence could be used to identify if two different species have been created through speciation?

  They can no longer interbreed/ produce fertile offspring.