The complementary strand of DNA of the following sequence is
ATCCGTTCG
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → TAGGCAAGC
The two strands of DNA are held together by hydrogen bonds between complementary base pairs. Because of their sizes and hydrogen bonding groups, the bases always pair in the same way:
Adenine (A) pairs with thymine (T), through two hydrogen bonds.
Guanine (G) pairs with cytosine (C), through three hydrogen bonds.
Writing the partner of each base in the given strand:
\( \displaystyle \mathrm{A\ T\ C\ C\ G\ T\ T\ C\ G} \)
\( \displaystyle \mathrm{T\ A\ G\ G\ C\ A\ A\ G\ C} \)
So the complementary strand is TAGGCAAGC.
Shortcut: The first base A must pair with T, which rules out Options (2) and (4). The fourth base C must pair with G, which rules out Option (3).
NCERT (2026-27 edition):
Structure of Nucleic Acids – …
