On what basis is DNA identified in genetic engineering?

Correct answer: On the basis of base sequence

The correct answer is A: DNA is identified on the basis of its base sequence. DNA is built from four bases—A, T, G, and C—and the order of these bases stores genetic information. A gene is recognised or selected by comparing its sequence with a known sequence, using complementary base pairing or other molecular detection methods. Thus, the sequence, not a superficial physical feature, provides the meaningful identity. Option A is correct because sequence determines the information and helps distinguish one gene or DNA region from another. Option B is wrong because cell colour is not the genetic code and cannot reliably identify a DNA sequence. Option C is wrong because the smell of water has no role in molecular DNA identification. Option D is wrong because soil hardness is unrelated to the bases in DNA. Memory cue: DNA information is written in the order of bases, like letters arranged into a message.