Point mutation

A genetic change affecting one nucleotide position, usually a single-base substitution and sometimes a one-base insertion or deletion.

Base substitution: A mutation that replaces one nucleotide base with another at a specific position in DNA or RNA. This is the most common form of point mutation.
Synonymous mutation: A coding-sequence substitution that does not change the encoded amino acid. Some point mutations leave a protein's amino-acid sequence unchanged.
DNA replication: The cellular process that copies DNA before cell division. Errors during copying are a major source of point mutations.
Sickle cell disease: An inherited blood disorder caused by a variant in the beta-globin gene that produces hemoglobin S. A single-base substitution in HBB causes the classic sickle hemoglobin change.
Indel: A genetic variant involving insertion or deletion of nucleotides in a DNA sequence. The broader indel category includes changes longer than one nucleotide.
Transition mutation: A base substitution between two purines or between two pyrimidines. Transitions are one of the two main substitution classes.
Missense mutation: A coding-sequence substitution that changes one encoded amino acid to another. A single-base substitution can replace one residue in a protein.
DNA polymerase: An enzyme that synthesizes DNA using an existing strand as a template. Its occasional copying errors can introduce mismatched nucleotides.
Huntington's disease: An inherited neurodegenerative disorder caused by expansion of CAG repeats in the HTT gene. Its mutation is a repeat expansion, not a single-position point mutation.
Structural variation: A genomic alteration that changes the arrangement or copy number of DNA segments, often across many bases. It affects larger genomic regions than a point mutation.

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