Point mutation

Gene mutation in which only a single nucleobase is affected by a genetic change. It is therefore a special case of gene mutation (see mutation below) and thus also of structural chromosome aberration.

The following point mutations are distinguished:

• Substitution: Here, one base of the DNA is exchanged for another. If this exchange occurs in a coding region, an altered mRNA is transcribed. This leads to an altered protein, which may no longer be able to carry out its tasks or may no longer be able to carry them out completely, depending on the location of the mutation or substituted amino acid. An example of a point mutation in humans is sickle cell anemia.
• A distinction is made between 2 types of substitution:
  • Transition:substitution of a purine base for a purine base or a pyrimidine base for a pyrimidine base.
  • Transversion: substitution of a purine base for a pyrimidine base or vice versa.
• For coding sequences, substitution can be divided into the following categories:
  • Nonsense mutation (sense-distorting mutation): codes for a stop in translation
  • Missense mut ation (mutation that changes the meaning): coding for a different amino acid
  • Silent mut ation: coding for the same amino acid
• Deletion: This is the loss of a base. The subsequent bases move up, which shifts the reading frame of the subsequent codons.
• Insertion: This involves the gain of a base. The subsequent bases move up in the reading direction.