DNA base pairing rules state that adenine (A) pairs with thymine (T) via 2 hydrogen bonds, and cytosine (C) pairs with guanine (G) via 3 hydrogen bonds. Therefore, for the given sequence ATGCTTCA, the complementary sequence is determined as follows:
Original Strand: A T G C T T C A
Complementary Strand: T A C G A A G T
This follows from the complementary base pairing rules.