突变产生的机理 Purine and pyrimidine Common forms Rare forms 0- Proton shift bases exist in different forms called tautomers Thymine (互变异构体) (a)a tautomeric shift NH2 Guanine occurs when a proton changes its position Cytosine resulting in a rare tautomeric form Adenine A Genetics ch1210Genetics Ch12.10 二、突变产生的机理 • Purine and pyrimidine bases exist in different forms called tautomers (互变异构体). • (a) A tautomeric shift occurs when a proton changes its position, resulting in a rare tautomeric form