1) An alteration in DNA sequence caused by a single nucleotide base change, insertion, or deletion.

2) A gene mutation involving the substitution, addition, or deletion of a single nucleotide base.

3) A point mutation is when a single base pair is altered. Point mutations can have one of three effects. First, the base substitution can be a silent mutation where the altered codon corresponds to the same amino acid. Second, the base substitution can be a missense mutation where the altered codon corresponds to a different amino acid. Or third, the base substitution can be a nonsense mutation where the altered codon corresponds to a stop signal.