A point mutation is a type of mutation that causes the replacement of a single base pair with another pair. There are several types of point mutations:

• nonsense mutations: codes for a stop, which can truncate the protein
• missense mutations: codes for a different amino acid
• silent mutations: codes for the same amino acid, so has no effect

For example, sickle-cell anemia 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.