Variation, evolution and mutations (pg. 67-69)

• Most variation in animals is caused by a mixture of genetic and environmental factors.
• Characteristics caused by the environment:

  1. A baby's weight can be affected by the mother's diet.
  2. Having a poor diet whilst growing up can stunt your growth.
• Characteristics caused by genes and the environment:

  1. Health.
  2. Intelligence.
  3. Sporting ability.
• Factors that cause environmental variation in plants:

  1. Sunlight.
  2. Moisture level.
  3. Temperature.
  4. The mineral content of the soil.
• Theory of evolution: Life began as simple organisms from which more complex organisms evolved.
• The resources that organisms need to survive are limited and individuals have to compete for these.
• "Survival of the fittest": organisms with the most suitable characteristics for the environment will be more succesful competitors and so will have a better chance of survival.
• Succesful organisms will have an increase chance of breeding and passing on their genes. This means that a greater proportion of individuals in the next generation will have the better alleles, and so the characteristics, that help survival.
• Over many generations, the characteristic that increases survival becomes more common in the population, making the species become better and better able to survive: they become more adapted to their environment.
• The individuals who are less suited to an environment are less likely to survive than those that are better suited, and so have less chance to pass their alleles on.
• A mutation is a rare, random change in an organism's DNA that can be inherited.
• Mutations change the sequence of the DNA bases in a gene, which produces a genetic variant. As the sequence of DNA bases codes for the sequence of amino acids that make up a protein, mutations to a gene sometimes lead to changes in the protein that it codes for.
• A mutation in the gene that codes for an enzyme could lead to a change in the shape of the enzyme's active site - altering its function. A mutation could also stop the production of the enzyme altogether.
• Mutations can lead to a different phenotype, increasing variation.
• Most mutations have no effect on the phenotype - they're neutral. For example, if the mutation occurs in an unimportant region of the DNA, or if a mutated codon still codes for the same amino acid, the protein's structure and function will be unaffected.
• A mutation will usually have no effect if it occurs in a recessive allele.
• Some mutations have a small effect on the phenotype. This happens when the change in amino acid only has a slight effect on the protein's structure and function - so that the individual's characteristics are only altered very slightly.
• Very rarely, a mutation will have a significant effect on the phenotype. For example, it might result in a very different protein which can no longer carry out its function. These mutations can be harmful (such as those which lead to cancer) or beneficial (giving a survival advantage).
• Mutations can happen spontaneously - when a chromosome doesn't copy itself properly.
• The chance of mutation is increased by exposing yourself to:

  • ionizing radiation.
  • chemicals called mutagens.
• Bacteria can evolve and become antibiotic-resistant.
• 'Superbugs' are bacteria that are resistant to most known antibiotics.