Frameshift Mutation
சட்டக இடப்பெயர்ச்சி சடுதிமாற்றம்
A single base pair shift is not a minor error; it is a catastrophic rewrite of the genetic code. If you think the ribosome ignores a single missing nucleotide, you are failing the exam. Biology is digital, not analog.
The idea
Frameshift mutation occurs due to the insertion or deletion of one or two base pairs in the DNA sequence. This alters the reading frame from the point of mutation, resulting in a completely different sequence of amino acids. However, the insertion or deletion of three or its multiples of bases adds or removes one or more codons, leaving the reading frame downstream unaltered.
Why it matters
It is a consequence of errors in DNA replication or damage, demonstrating the necessity of the triplet reading frame for correct protein synthesis.
NEET lens
NEET focuses on the 'multiple of three' rule. Expect questions asking whether a specific mutation alters the reading frame or just adds/removes an amino acid. Do not confuse point mutation with frameshift mutation. Memorize that 3-base changes preserve the frame; 1 or 2-base changes destroy it.
Clinical significance
Frameshift mutations are the primary cause of Duchenne Muscular Dystrophy and Tay-Sachs disease. These mutations lead to the production of non-functional, truncated proteins that fail to perform essential cellular tasks. The body cannot compensate for such fundamental errors in translation.
Introduction
A frameshift mutation is the insertion or deletion of one or two bases in a gene, which changes the reading frame from that point onwards.
Core concept
Because codons are read contiguously in triplets, adding or deleting one or two bases shifts every following codon, so the amino acid sequence after the mutation changes completely (and often a premature stop codon appears). Inserting or deleting three bases (or multiples of three) adds or removes one (or more) amino acids but keeps the reading frame from that point onwards. Point mutation = change in a single base pair (e.g. sickle-cell anaemia: GAG → GUG, Glu → Val at the 6th position of the beta-globin chain).
Go deeper
Classic sentence example: RAM HAS RED CAP → delete one letter → RAM ASR EDC AP (meaningless); delete three letters → RAM RED CAP (still meaningful, just shorter).
From Class 10
Imagine a sentence of three-letter words. Remove one letter and every word after it becomes nonsense — that is a frameshift.