Transzverziós

Transzverziós, in genetics often referred to as a transversion, is a nucleotide substitution in DNA or RNA in which a purine base (adenine or guanine) is replaced by a pyrimidine base (cytosine or thymine), or vice versa. In other words, purine-to-pyrimidine or pyrimidine-to-purine swaps occur. The common directional possibilities include A↔C, A↔T, G↔C, and G↔T, among their reverse forms. This is distinct from transitions, where substitutions occur within the same chemical class (purine to purine or pyrimidine to pyrimidine).

Frequency and causes vary across genomes. Transversions are typically less frequent than transitions in many organisms. They can arise from exposure to mutagens, oxidative damage, or replication errors. Certain mutational processes, such as alkylating agents or radical damage, tend to produce transversions more readily than transitions. Regions with CpG methylation followed by deamination predominantly generate transitions, making transversions relatively more informative for some mutational spectra.

Impact and applications are context-dependent. In coding sequences, transversions are more likely than transitions to cause amino acid changes, potentially contributing to functional divergence of proteins. In evolutionary and phylogenetic studies, transversions provide complementary information to transitions, especially at deeper evolutionary timescales where transitions may saturate. Substitution models used in phylogenetics often treat transitions and transversions with different rates (for example, the Kimura two-parameter model), reflecting their distinct mutational dynamics.

Terminology: In Hungarian, the term transzverziós mutáció describes this type of nucleotide change. The concept is a standard element of mutational spectra and evolutionary genetics.