Question

Determine the correctness or otherwise of the following Assertion [a] and the Reason [r].
Assertion [a]: Chromosome mutations can change the structure of chromosomes.
Reason [r]: All chromosome mutations arise due to nondisjunction of chromosomes during mitosis or meiosis.

• A. Both [a] and [r] are false
• B. [a] is true but [r] is false
• C. Both [a] and [r] are true and [r] is the correct reason for [a]
• D. Both [a] and [r] are true but [r] is not the correct reason for [a]

Hint:

Nondisjunction → numerical abnormalities (e.g., Down’s syndrome).
Structural mutations → caused by chromosome breakage and rearrangements.

Answer 1

The Correct Option is B

Step 1: Assertion [a] is true because chromosome mutations can indeed alter the structure (e.g., deletions, duplications, inversions, translocations).
Step 2: Reason [r] is false because not all chromosome mutations are due to nondisjunction. Nondisjunction leads mainly to changes in chromosome number (aneuploidy), not structure. Structural mutations arise from breakage and improper repair of chromosomes.
Step 3: Thus, [a] is true but [r] is false. Correct option is (B).