UPSC Prelims 2001 Q129: Science & Technology – Biotechnology & Genetics
Which of the following features of DNA makes it uniquely suited to store and transmit
genetic information from generation to generation?
- (a) Complementarity of the two strands
- (b) Double helix
- (c) Number of base pairs per turn
- (d) Sugar phosphate backbone
Answer: (a) Complementarity of the two strands
Explanation
Feature of DNA that suits it to store and pass on genetic information
| Feature | Role |
|---|---|
| Complementarity of the two strands | A pairs with T, G with C — each strand is a template for a new copy |
| Double helix | Shape; stable structure, but not the copying mechanism itself |
| Base pairs per turn | About 10 — a structural detail |
| Sugar-phosphate backbone | Gives strength; carries no information |
Because the two strands are complementary, each one holds all the information needed to rebuild the other. During semi-conservative replication each strand serves as a template, so genetic information is copied faithfully from generation to generation.
Answer: (a) Complementarity of the two strands.
Why each option is right or wrong
- (a) CORRECT. Complementary base pairing allows exact copying of genetic information.
- (b) Incorrect. The double helix is the shape; pairing is what permits copying.
- (c) Incorrect. The number of base pairs per turn is a structural detail.
- (d) Incorrect. The backbone gives strength but holds no information.
Key point
Meselson and Stahl (1958) proved DNA replication is semi-conservative.
Remember
DNA is copied faithfully because its strands are complementary.
Common mistakes
- Choosing the famous double helix as the answer.
- Thinking the backbone carries information.
- Forgetting how replication uses each strand as a template.
Exam tip
Ask what makes copying possible: base pairing.
Sources
- NCERT Class XII — Biology, chapter 'Molecular Basis of Inheritance'
- J. D. Watson and F. H. C. Crick — 'Molecular Structure of Nucleic Acids', Nature, 1953