Question

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): The hybrid cells formed by the fusion of two unrelated diploid protoplasts combine a set of three genomes from the parents.
Reason (R): Partial or complete elimination of nuclear genome before regeneration leads to the formation of cybrid plants.
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:

Hybrid = Nucleus A + Nucleus B.
Cybrid = Nucleus A + Cytoplasm (A + B).
If two diploids ($2+2$) meet, they make a 4n hybrid, not a 3n one.

Answer 1

The Correct Option is D

Concept: Somatic hybridization involves the fusion of protoplasts to create new genetic combinations. Depending on how the nuclei interact, the result can be a true hybrid or a cybrid.

Step 1: Evaluating the Assertion (The Error).
Assertion (A) states that fusing two unrelated diploid ($2n$) protoplasts combines a set of "three genomes." This is mathematically incorrect. When two diploid cells ($2n + 2n$) fuse, they initially form a tetraploid ($4n$) heterokaryon, combining four sets of genomes (two from each parent), not three.

Step 2: Evaluating the Reason.
Reason (R) is correct. A "Cybrid" (cytoplasmic hybrid) is formed when the nucleus of one parent is lost (either naturally or through irradiation) while the cytoplasm (chloroplasts/mitochondria) of both parents is retained. The partial or complete elimination of one nuclear genome before the cell regenerates into a plant is the definition of cybridization.

Step 3: Conclusion.
Since the mathematical claim in the Assertion is false but the biological description of cybrid formation in the Reason is true, option (4) is the correct choice.