Compare the causes, processes and effects of different types of mutation

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Compare the causes, processes and effects of different types of mutation, including but not limited to:

  • point mutation
  • chromosomal mutation

Point Mutation:

  • Addition, Deletion or substitution in a single nucleotide base pair in DNA or RNA.
  • Causes:
    • UV light and other higher frequency lights that can ionize electrons.
    • Reactive oxygen free molecules formed as a result of cellular metabolism.
  • Processes:
    • Base Substitution is a process of point mutation where one base is replaced by another. Can occur in two ways:
      • Transitions are mutation types where a purine is replaced by another purine and a pyrimidine is replaced by another pyrimidine.
      • Transversions occur when a purine can be replaced by either another purine or a pyrimidine and a pyrimidine can be replaced with another pyrimidine or a purine.
    • In case of Nonsense Mutation occurs when a nucleotide substitution creates a combination for stop codon ending translation in an earlier stage.
    • Silent Mutation is a type of point mutation in which, even if a base is substituted, the resulting codon codes for the same amino acid it would in the non-mutated configuration.
    • Point mutations can also occur due to Insertion or Deletion of bases in the mRNA transcript.
  • Effects:
    • Point Mutations cause a number of disorders some of which have been discussed below:
      • Cystic Fibrosis:
        • Results in the loss of the amino acid phenylalanine and causes an incorrectly folded protein. (This deletion is not a frameshift mutation because three bases next to each other are deleted, and all the other amino acids in the chain remain the same.)
      • Sickle Cell Anaemia:
        • Recessive disorder caused by a single substitution in the gene that creates haemoglobin.
        • When people have two copies of this mutation, it results in thin sickle-shaped blood cells that sometimes cannot carry oxygen properly.
      • Colour Blindness:
        • People who are colour blind have mutant genes that causes disability in red and green cones in cone cells. Thus, they cannot distinguish between red and green colour.

Chromosomal Mutations:

  • Structural or numerical changes in chromosome.
  • Differ from gene mutation and in many cases creates a more dangerous affect.
  • Causes:
    • Defective and uncontrolled cell division.
    • Exposure to harmful radiations.
    • Instability in chemical entities in the body that control biological processes.
  • Process:
    • Chromosomal Translocation:
      • A portion of one chromosome detaches and is transferred to another chromosome.
    • Deletions:
      • A portion of the chromosome is missing or deleted.
      • Can be caused by errors in the crossover of chromosomes during meiosis.
      • A single base pair to an entire piece of nucleotide or any number of nucleotides can be deleted causing loss of genetic material.
    • Duplications:
      • A portion of the chromosome is duplicated, resulting in extra genetic material.
    • Inversions:
      • A portion of the chromosome has broken off, turned upside down, and reattached within itself, therefore the genetic material is inverted.
    • Insertions:
      • A portion of one chromosome has been deleted from its normal place and inserted into another chromosome.
    • Rings:
      • A portion of a chromosome has broken off and formed a circle or ring. This can happen with or without loss of genetic material.
    • Aneuploidy:
      • Numerical chromosomal aberration which can be of the following types:
        • Monosomy: a chromosome is missing from a pair
        • Trisomy/Tetrasomy: more than two chromosomes exist in a pair
      • Occurs due to defective separation of homologous chromosomes during cell division.
    • Polyploidy:
      • State of having more than two complete sets of chromosomes.
      • Commonly found in plants and occur rarely in humans.
  • Effects:
    • Partial deletion in the short arm of chromosome 4 causes Wolf–Hirschhorn syndrome that causes a distinct craniofacial phenotype and intellectual disability.
    • Deletion in the q arm of chromosome 11 causes Jacobsen syndrome which is a congenital disorder.
    • Down’s Syndrome, a disorder related to physical growth delays, characteristic facial features, and mild to moderate intellectual disability is caused due to the presence of an extra copy of chromosome 21, also known as trisomy 21.
    • Inversions are mostly harmless but sometimes, they might be responsible for increased risk for miscarriage or infertility.
    • Turner Syndrome is a disorder in the sex chromosome of females where their sex chromosome pair is monoploid (which means, only one X chromosome is present).
    • In Kleinfelter syndrome males have an extra X chromosome in their sex chromosome pair.

Extract from HSC Biology Stage 6 Syllabus. © 2017 Board of Studies NSW.