Genetics / mutation · BEGINNER LESSON
Insertion or deletion
An insertion or deletion is a mutation in which one or more nucleotides are added to or removed from DNA. When it happens in a protein-coding region, the effect depends on whether the number changed is a multiple of three.
What it is
An insertion adds nucleotide(s) to a DNA sequence, and a deletion removes nucleotide(s). A nucleotide is one of the building blocks of DNA. These changes are a type of mutation, meaning a change in the nucleotide sequence of a genome region. They can occur anywhere in the genome, not only in genes.
[1] Nature of Mutations in Genetic Disorders - NCBI - NIH [2] Mutation, Repair and Recombination - Genomes - NCBI - NIH
What is measured or observed
Scientists observe the size and position of the added or missing DNA. Small events may involve one or a few nucleotides, while larger events can remove or add longer segments. In coding regions, the key measurement is whether the number of nucleotides changed is a multiple of three, because three nucleotides form one codon, a DNA triplet that specifies an amino acid during protein making.
[1] Nature of Mutations in Genetic Disorders - NCBI - NIH [2] Mutation, Repair and Recombination - Genomes - NCBI - NIH
How they happen
Several mechanisms can create insertions or deletions. During DNA replication, the copying machinery can slip on repeated sequences, causing a short stretch to be copied twice or skipped. Recombination between repeated DNA segments can also produce changes. Some larger insertions may come from retrotransposition, a process where genetic material is copied through an RNA intermediate and inserted elsewhere. Broken DNA ends can also be joined imperfectly by non-homologous end joining, or NHEJ, a repair process that joins DNA ends without needing matching sequence.
[1] Nature of Mutations in Genetic Disorders - NCBI - NIH [2] Mutation, Repair and Recombination - Genomes - NCBI - NIH [3] The origin, evolution, and functional impact of short insertion ...
Why they matter
If the insertion or deletion in a coding region is not a multiple of three, the reading frame shifts. The ribosome then groups the remaining nucleotides into different codons, changing the amino acid sequence downstream and often causing an early stop signal. If the change is three nucleotides or a multiple of three, whole codons are added or removed, so the reading frame stays the same, although the protein can still lose or gain important amino acids. Larger changes usually have stronger effects on gene structure and function.
[1] Nature of Mutations in Genetic Disorders - NCBI - NIH [2] Mutation, Repair and Recombination - Genomes - NCBI - NIH
Limitations and evidence level
The sources describe several mechanisms, but they do not say one mechanism explains all insertions or deletions. Evidence is strongest for short repeat-associated events being common, especially polymerase slippage in repeated DNA, while other mechanisms contribute to some larger or more complex cases. The exact outcome depends on location, size, and whether coding sequence is affected.
[1] Nature of Mutations in Genetic Disorders - NCBI - NIH [2] Mutation, Repair and Recombination - Genomes - NCBI - NIH [3] The origin, evolution, and functional impact of short insertion ...
SEE THE IDEA
How an insertion or deletion can affect DNA
One or more nucleotides are added or removed.
Slippage, recombination, retrotransposition, or imperfect repair can create the change.
If the change is not a multiple of three, the reading frame shifts.
Amino acids downstream change, or codons are added/removed without a shift.
A mutation mechanism creates a DNA change; its size and position determine whether protein reading is preserved or disrupted.
Insertions and deletions are defined by the DNA change first, then interpreted by where they occur and how many nucleotides are involved.
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Sources and further reading
This general lesson was generated from public source material. It explains a concept; it does not interpret a private paper or provide medical advice.