Definition for Frameshift mutation
From Biology Forums Dictionary
1) A mutation that involves the addition or deletion of nucleotides that are not in multiples of three nucleotides.
2) This type of mutation occurs when the addition or loss of DNA bases changes a gene's reading frame. A reading frame consists of groups of 3 bases that each code for one amino acid. A frameshift mutation shifts the grouping of these bases and changes the code for amino acids. The resulting protein is usually nonfunctional. Insertions, deletions, and duplications can all be frameshift mutations.