Question

Everyone knows that a pairs with t, and g pairs with

c. on occasion, however, mis-pairings may occur. which mis-pairing would most closely resemble a normal pair (assume that all bases are in their most common unmodified form)?

Answer 1

It's more common to happen transitions( even though there are less possibilities) because of the shape of the molecules.
Transitions exchange bases of similar shape (swaps a purine for a purine or a pyrimidine for a pyrimidine), whereas transversions exchange bases of different shape( swaps a purine for a pyrimidine (or vice versa)).

A and G are purines, C and T are pyrimidines.

possible transversions A-C, A-T, T-G, G-C
transitions are A-G or C-T

answer: AG or CT pairs