Gene mutations

• Gene mutations


  Involves a change in DNA base sequence of chromosomes, order of DNA bases in a gene determines order of amino acids in a particular protein.

  A mutation occurs in a gene, sequence of amino acids it codes for could be altered.
• Effects of mutations

  • degenerate nature of genetic code means that some amino acids can be coded for by more than one DNA triplet.
  • Not all substitution mutations will result in a change to amino acid sequence of protein, some substitutions will still code for same amino acids
• Deletions

  • Deletion of a base changes the number of bases present causing a shift in all base triplets after it
• Mutagenic agents

  • mutations occur spontaneously, when DNA is misread during replication.
  • Mutagenic agents increase rate of mutations, e.g UV radiation, ionising radiation, viruses etc.
  • Increasing probability of mutation occuring
• Chromosome mutation caused by errors in meiosis, leading to inherited conditions as errors already present in gametes. e.g CHROMOSOME NON DISJUNCTION, failure of chromosomes to separate properly
• Down syndrome: caused by an extra copy of chromosome 21

  • Non disjunction mean chromosome 21 fails to separate properly, so one cell gets an extra copy of 21 and another gets none
  • When gamete with extra chromosome fuses with another gamete, zygote will have three copies of chromosome 21