Mutations by gjjur4356


• Inheritable errors made in DNA during
• 3 broad groups:
  – Beneficial
  – Deleterious
  – Neutral
• Most mutations are neutral, either because
  they occur in introns, or because of the
  redundancy inherent in our genome
     Categories of Mutations
1. Point mutations
  – Mutations at a specific base pair on the
2. Chromosomal mutations
  – One DNA fragment is moved from one site on
    the genome to another
               1. Point mutations
Type              Result(s)
Substitution      1. Silent/neutral mutation
                    •   New codon codes for same or
                        similar AA as original; protein is
                  2. Missense mutation
                    •   New codon codes for different AA;
                        protein is slightly altered
                  3. Nonsense mutation
                    •   New codon is a stop codon,
                        creating a non-functional protein
            1. Point mutations
Type        Result(s)
Insertion   Frameshift mutation
or          • Change in reading frame of the
Deletion       mRNA*
            • Many AAs changed
            • Drastically altered protein
            *unless whole codon is inserted/deleted
   2. Chromosomal Mutations
Type                      Result(s)
Translocation             •   Inactivation of genes
  – Usually occurs        •   Creation of fusion
  between two non-            protein with completely
                              altered function
                              – Common translocation is
  – A fragment of one
                                the exchange of a
                                promoter from one gene
  switches places with
                                with the promoter of a
  a fragment of another
                                different gene
    2. Chromosomal Mutations
Type                    Result(s)
Inversion               •   Inactivation or
  – chromosome section      disruption of genes
  that has reversed its •   Gene may come under
                            alternate control
    2. Chromosomal Mutations
Type                  Result(s)
Amplification or mass •   Either dramatically
deletion                  increases or decreases
                          amount of gene product
• Transposons, a.k.a transposable elements
  or “jumping genes,” are sections of DNA
  that naturally jump from one area of the
  genome to another
• They have effects similar to translocations
• They were discovered by Barbara
  McClintock, for which she was awarded the
  Nobel prize
   Causes of Mutations

1. Spontaneous mutation
2. Induced mutation
     Spontaneous Mutations
• Caused by errors during DNA replication
  that are go uncorrected
• Can also be caused by errors made during
  crossover in meiosis
         Induced Mutations
• Caused by mutagens (mutagenic agents)
• 2 kinds of mutagens:
  – Physical mutagens physically damage DNA
  – Chemical mutagens alter the molecular
    structure of DNA without damaging it
• Note: mutagens that also cause cancer
  are called carcinogens
         Physical Mutagens
• For example, radiation
       Chemical Mutagens
• For example, base analogs

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