Depurination is one of the spontaneous lesions that can lead to mutations.
In depurination, there is a loss of the adenine or guanine base from the DNA (deoxyribonucleic acid) backbone. A complementary base cannot be specified by the apurinic site. Hence, replication is blocked.
Sometimes replication occurs with a base inserted randomly opposite to the apurinic site. Most of such cases will result in mutations.
Deamination of cytosine results in uracil. Uracil will be paired with adenine if it is not repaired and will result in transition mutation. Also, deamination of 5-methylcytosine thymine mostly leads to C-T transition mutation.
If oxidatively damaged bases pair with adenine, transversion mutations can result. Spontaneous indel mutations are resulted due to errors happening during DNA replication.