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Types of genetic variation

Single base-pair substitution

These are also known as single nucleotide polymorphisms (SNPs) and can be any nucleic acid substitution:

  1. Transition
    • interchange of the purine (Adenine/Guanine)
    • or pyrimidine (Cytosine/Thymine) nucleic acids
  2. Transversion
    • interchange of a purine and pyrimidine nucleic acid (Figure 4)

Move the slider to the right to see a SNP:

Figure 4 SNPs result from the substitution of a single base-pair. In this example we have a transversion event substituting a Thymine nucleic acid in place of a Guanine.

Insertion or deletion, also known as ‘indel’

Insertion or deletion of a single stretch of DNA sequence that can range from two to hundreds of base-pairs in length (Figure 5).

Insertion adds bases and deletion results in their removal.
Figure 5 Indels affect a string of base-pairs. In this example the insertion string shows that GTA has been inserted, and the deletion string shows a deletion of CA.

Structural variation

Typically used to describe genetic variation that occurs over a larger DNA sequence. This category of genetic variation includes both copy number variation and chromosomal rearrangement events.

Discover the five most common types of structural variants in this drag-and-drop game: