Question

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): Chromosome number may change under prolonged plant tissue culture regimes.
Reason (R): Endosperm cells are triploid in nature.
In the light of the above statements, choose the most appropriate answer from the options given below:

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

In Assertion-Reason questions, always ask: "Does the second sentence tell me why the first sentence happened?" Here, they are just two unrelated facts.

Answer 1

The Correct Option is B

Concept: This question evaluates knowledge of chromosomal instability in tissue culture (Somaclonal variation) and basic plant biology regarding the endosperm.

Step 1: Evaluating the Assertion.
Assertion (A) is correct. During prolonged in vitro culture, especially in the callus phase, cells often undergo chromosomal rearrangements, polyploidy, or aneuploidy. This phenomenon is a major source of somaclonal variation.

Step 2: Evaluating the Reason.
Reason (R) is also correct. In angiosperms, the endosperm is formed by the fusion of one male gamete ($n$) with two polar nuclei ($n+n$), resulting in a triploid ($3n$) tissue.

Step 3: Determining the Relationship.
While both statements are scientifically true, the triploid nature of endosperm cells (a natural reproductive feature) does not explain why chromosome numbers change during artificial tissue culture (which is caused by the stress of the in vitro environment and hormonal imbalances). Therefore, (R) is not the explanation for (A).