Chemical Alteration of Nucleotide Structure . Most direct-acting mutagens transform the chem. Transitional mutations . A purine is replaced by another purine or a pyrimidine is replaced. G transition is result .
Purine is replaced by a pyrimidine or vice versa b.
Not very common because most transversions don't fit properly into the DNA helix. In spite of this a few mutagens believed to cause transversion. Back to Molecular Genetics .