5.2.2 mutations & variations

• The effect of mutation depends on where on a chromosome it happens: on a region of coding DNA or non-coding DNA
• Non-coding DNA

  • doesn't affect proteins produced by transcription and translation
  • but it does affect the transcription process by either "switching on" or "switching off" certain genes
  • "switched on" genes mean they are being expressed
  • causes an increase or decrease in amount of protein being produced
• non-coding DNA alters gene expression ("on" or "off" genes)
• Coding DNA

  • causes changes in a protein produced by DNA transcription and translation
  • can affect the protein's structure and/or function
  • Cystic Fibrosis is caused by a mutation in a region of coding DNA
• Variation - the differences in characteristics of individuals
• Variation may be a result of differences in:

  • the environment - the conditions in which the organism was developed
  • genetics and environment - a combination of genetic and environmental causes
  • genetics - inherited genes. all genetic mutation is the result of mutations, some of which are then inherited and passed onto the next generation
• How can mutations lead to human evolution?

  • Most mutations (permanent changes in nucleotide sequences of DNA) do not affect the phenotype.
  • But if a mutation creates a new phenotype that is better adapted to environmental changes (than the rest of the population), the mutation is likely to spread throughout the population over a small number of generations.
  • For example, over time the size of the human brain has increased, as those born with a bigger brain were found to be at a survival advantage.
• Types of variation

  • continuous - affected by a combination of genes and the environment. values of continuous variation usually fit a bell-shaped curve
  • discontinuous - affected by only genes. individuals fall into distinct categories
• Fill the gaps

  A) genes and the environment

  B) bell-shaped

  C) categories

  
• Which type of variation is controlled by both genes and the environment?

  continuous variation
• Some regions of DNA do not encode protein sequences. The term given to these sections is non-coding DNA. Non-coding DNA often plays a role in gene expression. So mutations that arise here may result in genes being switched on or off.
• Discontinuous variation

  • Individuals fall into a number of distinct categories. It is often determined only by genes.
• Continuous variation

  • No limits on the values that this type of variation can take. It is normally affected by a combination of genes and the environment.