In DNA, adenine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G). These base pairing rules are known as complementary base pairing. So, if you have a template strand of DNA with the sequence "ATCG," the new strand that is synthesized will have the sequence "TAGC" because A pairs with T, T pairs with A, C pairs with G, and G pairs with C.
