transversioner

Transversioner, commonly referred to as transversions, are a class of DNA base substitutions in which a purine is replaced by a pyrimidine or vice versa. In DNA, purines are adenine and guanine, while pyrimidines are cytosine and thymine. A transversion therefore includes substitutions between purine and pyrimidine bases, such as A to C, A to T, G to C, and G to T, as well as the reverse changes C to A, C to G, T to A, and T to G. By contrast, transitions are substitutions within the same chemical class, such as A to G or C to T.

Transversions are generally less frequent than transitions in many organisms, a pattern known as transition bias. Their occurrence can be influenced by mutational processes and DNA damage. For example, oxidative damage can generate 8-oxoguanine, which mispairs with adenine and can lead to G to T transversions; certain alkylating or hydrolytic lesions can also promote purine–pyrimidine substitutions.

Functional consequences depend on context. In coding regions, transversions are more likely than transitions to alter amino acid properties, increasing the chance of nonsynonymous changes or premature stop codons. In regulatory or noncoding regions they can affect motifs, splicing, or RNA structure.

In genomics and evolutionary biology, transversion rates and spectra contribute to mutation rate estimates, phylogenetic analyses, and studies of genome evolution. They are identified in sequencing data by classifying observed substitutions according to the nucleotide changes.