Explain frame-shift mutation.

(N/A) frame-shift mutation occurs due to the insertion or deletion of one or two base pairs in the $DNA$ sequence.
This causes a change in the reading frame from the point of insertion or deletion onwards.
If one or two bases are added or deleted,the entire sequence of codons downstream is altered,leading to the synthesis of a completely different polypeptide chain.
However,if three bases or a multiple of three bases are inserted or deleted,one or more codons are added or removed,but the reading frame remains unchanged after the site of mutation.
Such mutations are specifically referred to as frame-shift insertion or deletion mutations.