| − | 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. | + | 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 the beta [[hemoglobin]] gene, whereby a GAG codon is converted into GTG. The GTG then mistakenly encodes the [[amino acid]] valine instead of glutamic acid. | + | 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. |