Frameshift Mutation
Definition
A change in the reading frame of a coding sequence caused by an insertion or deletion of a number of nucleotides that is not a multiple of three. All codons downstream of the change are altered, usually producing a truncated or non-functional protein.
- Cause
- Insertion/deletion not a multiple of three
- Effect
- Shifts the downstream reading frame
- Typical result
- Truncated or non-functional protein
- Contrast
- In-frame indels (multiples of three) preserve frame
Common questions
Why does an insertion or deletion of exactly three nucleotides not cause a frameshift?+
The genetic code is read in triplet codons, so removing or adding a full codon's worth of nucleotides only adds or deletes one amino acid while every codon after it is still read in its original grouping, unlike a shift of one or two bases which throws off every codon downstream.
Why do frameshift mutations often produce a premature stop codon?+
Once the reading frame shifts, the ribosome reads a completely different, effectively random sequence of triplets from that point onward, and one of those out-of-frame triplets will statistically likely form a stop codon before the normal end of the gene is reached, truncating the protein.
How is a frameshift mutation relevant to forensic DNA profiling versus disease-gene analysis?+
Standard forensic STR profiling targets non-coding repeat regions and is not affected by frameshift logic, which applies to protein-coding sequences; frameshift mutations become relevant in forensic genetics mainly in the context of interpreting rare gene-based identity or medical-genetic evidence, not routine STR comparison.
Related terms
- DNA Polymerase
- The enzyme that synthesises new DNA by adding deoxyribonucleoside triphosphates complementary to the template strand. In humans, polymerase delta copies the lagging...
- Okazaki Fragment
- A short segment of DNA (100 to 200 nucleotides in eukaryotes) synthesised on the lagging template strand in the 5-prime to 3-prime...
- Point Mutation
- A change in a single nucleotide in the DNA sequence. A transition substitutes one purine for another or one pyrimidine for another...
- Semi-Conservative Replication
- The mode of DNA copying in which each daughter double helix retains one parental strand and acquires one newly synthesised strand, confirmed...
- Short Tandem Repeat (STR) Slippage
- Replication slippage at a repetitive locus where the template and nascent strands temporarily misalign. If the nascent strand slips forward, one repeat...