FIGURE 5-34 Deamination leads to point mutations. A spontaneous point mutation can be caused by deamination of 5-methylcytosine (C) to form thymine (T). If the resulting T·G base pair is not restored to the normal C·G base pair by base excision-repair mechanisms 1, it will lead to a permanent change in sequence (i.e., a mutation) following DNA replication 2. After one round of replication, one daughter DNA molecule will have the mutant T·A base pair and the other will have the wild-type C·G base pair.