Practice question

Transition mutation is subtype of base substitution where a purine is replaced by remaining purine (A↔G) or pyrimidine by remaining pyrimidine (C↔T), preserving ring type. Such changes arise from tautomeric mispairing and deamination events, for instance deamination of 5-methylcytosine producing thymine. Because purine-pyrimidine axis stays similar, helical distortion is minimal and lesions often escape detection by repair surveillance, leading to higher spontaneous frequency than transversions and influencing codon degeneracy patterns observed in molecular evolution. This principle illustrates essential molecular mechanisms governing replication fidelity and mutation fixation relevant for exam interpretation.