Step 1: Concept Overview:
The question tests the knowledge of matching chemical mutagen classes to their specific examples. A mutagen is defined as a physical or chemical agent that induces changes in an organism's genetic material, typically DNA.
Step 2: Detailed Matching:
Let's analyze each mutagen class in List-I to determine the correct matches:
A. Alkylating agent: These agents add alkyl groups (e.g., -CH₃, -CH₂CH₃) to nucleotide amino or keto groups, leading to altered base-pairing. A prime example is Mustard gas. Therefore, A corresponds to III.
B. Base analog: These molecules resemble normal DNA purine and pyrimidine bases. They can be incorporated into DNA during replication, causing mispairing. 5-Bromouracil, a thymine analog, fits this description. Thus, B corresponds to IV.
C. Intercalating agent: These flat molecules insert (intercalate) between DNA base pairs, distorting the double helix and potentially causing frameshift mutations during DNA replication. Acridine Orange exemplifies this class. Hence, C corresponds to I.
D. Deamination agent: These agents remove amino groups (-NH₂) from nucleotide bases. Nitrous acid (HNO₂) deaminates cytosine to uracil and adenine to hypoxanthine, resulting in incorrect base pairing. Therefore, D corresponds to II.
Step 3: Conclusion:
The correct matches are A-III, B-IV, C-I, D-II, which aligns with option (D).