Module 6

• Mutation


  A change in a gene or chromosome.
• Mutagen


  things that cause mutations in dNA
• 3 types of mutagens are

  physical, chemical and biological mutagens
• Physical mutagens include


  X-rays, Gamma rays and UV light
• how do X-rays and Gamma rays damage DNA

  they are ionising radiation that produces free radicals in DNA. These can cause the DNA to break
• what are examples of ionising radiation


  x rays and gamma rays
• what is an example of non-ionising radiation

  UV light
• how does UV light damage DNA?

  causes formation of thymine dimers. A kink in the DNA forms which will block/disrupt DNA replication, increasing errors in the DNA molecules produced.
• Three types of chemical mutagens are

  intercalating agent, base analogue, reacting chemicals
• intercalating agent


  The chemical slips in between two base pairs, altering the morphology of DNA at that position. Increases chance of error during replication
• Base analogue


  Are pretend nitrogen bases, and their insertion result in errors in DNA replication
• reacting chemicals


  Chemicals that react directly with the nitrogenous bases, chemically modifying them. (Cigarette smoke contains these, thus cigarette smoke damages DNA)
• Biological mutagens include


  retroviruses, transposable genetic elements
• Retroviruses


  A virus that inserts its genetic material into the DNA of a host cell, resulting in mutations
• transposable genetic elements


  jumping genes. Sections of DNA that can move around among chromosomes. These alter the sequence of DNA.
• Impacts of mutations on organisms

  Can be positive: the mutation makes the protein more effective. Can be bad: the mutation makes the protein non-functional, more damaging and result in cancer. Can be neutral: the mutation has no effect on the protein.
• All mutations fall into two basic categories:

  gene mutations and chromosomal mutations
• chromosomal mutations are


  changes in chromosome number
• Nondisjunction


  Error in meiosis in which sister chromatids fail to separate. Can result in an organism having extra or less chromosomes.

  
• What happens when someone has three of chromosome 21.

  Down's syndrome (trisomy 21)
• 4 types of chromosomal mutations

  deletion, duplication, inversion, translocation
• chromosomal deletion


  loss of all or part of a chromosome
• chromosomal duplication


  Parts or several parts of gene have been duplicated
• chromosomal inversion


  One or more parts reverse direction
• chromosomal translocation


  part of chromosome breaks off and attaches to another.
• XXY sex chromosomes results in

  Klinefelter syndrome
• XO sex chromosomes results in

  Turner's syndrome

  
• Karyotypes tell us about

  sex, chromosomal disorders
• Karyotypes cannot tell us about

  whether insertion, deletion, translocation or inversion have occurred. Cannot tell DNA sequence and cannot determine phenotype.
• Gene mutations are


  alterations in the normal sequence of bases within a gene.
• Point mutations are


  chemical changes in just one base pair of a gene
• point mutations include


  substitutions, insertions, deletions
• point Substitution


  one nucleotide replaces another

  
• point insertion


  a nucleotide is added

  
• point deletion


  a nucleotide is removed.

  
• silent mutation


  When the mutation has no effect. Multiple codons can code for the same amino acid.
• missense mutation


  A single amino acid is changed
• Example of missense mutation


  sickle cell anemia
• nonsense mutation


  creates premature STOP codon
• frameshift mutation


  when adding or removing nucleotide shifts the reading frame of the gene. Every codon beyond point of mutation is affected.