3.6 biology

• Mutation


  A random and spontaneous change in the structure of a gene, chromosome or number of chromosomes; only source of new alleles
• Neutral mutations


  • Mutations that have little effect on an organism
• Advantageous mutations


  • Mutations that provide an advantage to an organism and increase its chances of survival
• Disadvantageous mutations


  • Mutations that can be harmful and give the organism a disadvantage and so decrease its chance of survival
• Mutagenic agents


  A factor which increases the rate of mutation e.g. radiation and chemicals such as mustard gas
• Variation


  Differences in characteristics that can be seen between individual members of a species. This allows a population to evolve over time in response to changing environmental conditions
• Offspring


  The individuals produced by reproduction
• Natural selection


  Individuals that are poorly adapted to their environment are less likely to survive and reproduce. This means that their genes are less likely to be passed to the next generation. Given enough time, a species will gradually evolve
• Species


  Organisms with similar characteristics and with the ability to interbreed to produce fertile offspring
• Speciation


  Formation of two or more species from an original ancestral species
• Adaptation


  Feature of an organism that helps it to survive in its habitat
• Examples of isolation barriers during speciation


  • Geographical
  • Ecological
  • Behavioural
• Selection pressures


  Pressures that will affect natural selection and will affect if an organism survives or not
• Mutations


  1. A mutation is a random change to genetic material

  2. Mutations may be neutral, offer an advantage or a disadvantage

  3. Mutations are spontaneous and are the only source of new alleles
• Environmental factors which can increase the rate of mutation

  • Radiation (UV light and X-rays)
  • Chemicals (mustard gas)
• Process of Speciation


  1. Speciation occurs after part of a population becomes isolated

  2. Different mutations occur in each sub-population

  3. Natural Selection selects different mutations in each group, due to different selection pressures

  4. Each sub-population evolves until they become so genetically different that they are 2 different species