Point mutation

From Freepedia

A point mutation, or substitution, is a type of mutation that causes the replacement of a single base pair with another pair. Often the term point mutation also includes insertions or deletions of a single base pair. For coding sequences one can categorize such mutations as follows:

• nonsense mutations: code for a stop, which can truncate the protein.
• missense mutations: code for a different amino acid.
• silent mutations: code for the same amino acid.

For example, sickle-cell disease is caused by a single point mutation in the beta hemoglobin gene that converts a GAG codon into GTG, which encodes the amino acid valine rather than glutamic acid.

Point mutations that occur in non-coding sequences are most often without consequences, although there are exceptions. If the mutated base pair is in the promoter sequence of a gene, then the expression of the gene may change. Also, if the mutation occurs in the splicing seat of an intron, then this may interfere with correct splicing of the transcribed pre-mRNA.