Table 3. Illustration of the impact of frameshift mutations to the reading frame.

A deletion or an insertion of a DNA fragment somewhere in an upstream codon is shifting the reading frame for all codons downstream. For ±3 letters, the reading frame stays intact, hence this shift is not a frameshift mutation. The reading frame after +1 and −2 reading frame shifts is leading to the same read out, just as the −1 and +2 shifts lead to the same reading frame. XYZ hereby denote the (unknown) nucleotides that slip into the sequence due to the frame shift.

	Sequence		Triplets
Original sequence	AUCGUAGUCAAU	⟶	AUC GUA GUC AAU
Shift +1	XAUCGUAGUCAA	⟶	XAU CGUAGUCAA
Shift −2	CGUAGUCAAUXY	⟶	CGUAGUCAA UXY
Shift −1	UCGUAGUCAAUX	⟶	UCGAUGUCA AUX
Shift +2	XYAUCGUAGUCA	⟶	XYA UCGAUGUCA