Why cannot other bases join with the complementary base pairing?

Other bases cannot join with complementary base pairing due to the specific hydrogen bonding patterns and structural conformations required for base pairing. For instance, adenine pairs with thymine (or uracil in RNA) through two hydrogen bonds, while guanine pairs with cytosine through three hydrogen bonds. Bases that do not share these specific bonding properties or structural shapes cannot form stable interactions, leading to mismatches that destabilize the DNA structure. This specificity is crucial for the fidelity of DNA replication and transcription.