13.3.2

Mutations

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Mutations

Mutations are changes to the base sequence in the DNA. Mutations can be caused by addition, deletion and substitution of bases.

Mutations

Mutations

  • Mutations are changes to the DNA sequence.
  • Mutations are almost always harmful because they interrupt the normal functioning of a protein.
    • E.g. Cystic fibrosis is a genetic disorder caused by a mutation in the gene for a transmembrane protein.
Addition mutations

Addition mutations

  • Addition mutations are where one or more bases are added to the DNA sequence.
    • E.g. ATCGTT → ATCCGTT
      • In this example, a C is added in the middle of the DNA sequence.
Deletion mutations

Deletion mutations

  • Deletion mutations are where one or more bases are removed from the DNA sequence.
    • E.g. ATCGTT → ATCTT
      • In this example, the G is deleted from the middle of the DNA sequence.
Substitution mutations

Substitution mutations

  • Substitution mutations are where one or more bases are changed in the DNA sequence.
    • E.g. ATCGTT → ACCGTT
      • In this example, the first T is substituted for a C.

Causes of Mutation

Changes to the DNA sequence are known as gene mutations. Causes of mutation include:

DNA replication

DNA replication

  • When DNA is replicated, the bases in the DNA sequence are read and copied.
  • There can be errors in the replication process. These errors cause mutations.
  • Mutations caused in DNA replication are spontaneous.
Mutagenic agents

Mutagenic agents

  • Mutagenic agents can also increase the rate at which mutations occur.
  • Mutagenic agents include:
    • Chemicals (e.g. bromine and benzene).
    • Exposure to ionising radiation and ultraviolet radiation.
Chromosome mutations

Chromosome mutations

  • Chromosome mutations can also arise spontaneously during meiosis.
  • Chromosome mutations can affect the number of chromosomes in a developing zygote. This is called aneuploidy.
  • Meiosis is the production of haploid gametes. During meiosis, pairs of chromosomes are separated.
    • Non-disjunction is when chromosome pairs do not separate properly.
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Practice questions on Mutations

Can you answer these? Test yourself with free interactive practice on Seneca — used by over 10 million students.

  1. 1
    Which of the following statements about mutations are true?True / false
  2. 2
    Which of these is an addition mutation?Multiple choice
  3. 3
    Which of these is NOT a cause of mutations?Multiple choice
  4. 4
    Which of the following statements about mutations are true?True / false
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Genes

DNA Technology