An insertion or deletion involving
a number of base pairs that is not a multiple of three and consequently disrupts
the triplet reading frame, usually leading to the creation of a premature
termination (stop) codon and resulting in a truncated protein product
Definition from: GeneReviews
from the University of Washington and the National Center for Biotechnology Information
A frameshift mutation is a type of mutation involving the insertion or deletion of a nucleotide in which the number of deleted base pairs is not divisible by three. "Divisible by three" is important because the cell reads a gene in groups of three bases. Each group of three bases corresponds to one of 20 different amino acids used to build a protein. If a mutation disrupts this reading frame, then the entire DNA sequence following the mutation will be read incorrectly.