Frameshift mutation
Say it: FRAYM-shift myoo-TAY-shun
A frameshift mutation is an insertion or deletion of DNA bases, in a number not divisible by three, that shifts how the rest of a gene's codons are read.
Also: frameshift, frameshift variant, reading frame shift
Definition
What is a frameshift mutation?
A frameshift mutation is a change in a gene in which a number of bases that is not a multiple of three is inserted or deleted. The cell reads a protein-coding sequence in non-overlapping groups of three bases, called codons, starting from a fixed point, so adding or removing one or two bases shifts the reading frame. Every codon after the change is then read in the wrong grouping.
An analogy helps. In THE FAT CAT ATE THE RAT, deleting the first T gives HEF ATC ATA TET HER AT, which no longer makes sense. In a gene, the shifted frame puts a string of wrong amino acids into the protein and usually soon hits a stop codon by chance, cutting the protein short. The result is typically a protein that does not work. By contrast, inserting or deleting exactly three bases adds or removes a single amino acid and leaves the rest of the protein in frame.
Experiments with frameshift mutations in a virus helped Francis Crick and Sydney Brenner show that the genetic code is read in triplets. Frameshifts lie behind many inherited disorders, because even one extra or missing base can disable a gene.
Word parts
Where does the term “frameshift mutation” come from?
- mut-
- to changeLatin mutare
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Terms that go with it
- MutationA mutation is a lasting change in an organism's DNA sequence, ranging from a single altered base to large rearrangements of chromosomes.
- CodonA codon is a sequence of three nucleotides in DNA or messenger RNA that stands for one amino acid or tells the ribosome to stop.
- TranslationTranslation is the process in which a ribosome reads the codons of a messenger RNA and links amino acids in that order to build a protein.
- Messenger RNAMessenger RNA is the RNA copy of a gene that carries protein-building instructions from DNA to the ribosomes, where it is read in three-base codons.
- GeneA gene is a stretch of DNA that carries the instructions for making a protein or a working RNA molecule, and is the basic unit of heredity.
- ProteinA protein is a large molecule made of one or more chains of amino acids, folded into a specific shape that determines its job in the body.
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Checked against
Written for biofideX in plain words, after checking these references:
- NHGRI Talking Glossary: Frameshift Mutation
- MedlinePlus Genetics: What kinds of gene variants are possible?
- OpenStax Biology 2e, 15.1 The Genetic Code
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