Point mutation

From Conservapedia

A point mutation is the most limited type of mutation, whereby a single base nucleotide is replaced with another nucleotide. Sometimes the expression "point mutation" can also include the addition or subtraction of a single base pair, which is also referred to as an "indel".

The sickle-cell disease is caused by a single point mutation in one allele of the beta hemoglobin gene, whereby a CCT codon is converted into TCT. The TCT then mistakenly encodes the amino acid serine instead of proline.