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Question #45604

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The Question

Gametophytic self-incompatibility (GSI) in Nicotiana is controlled by a multiple allelic series at the S-locus. A plant with the genotype $S_1S_2$ is pollinated by a plant with the genotype $S_2S_3$ . Which of the following statements is INCORRECT regarding the physiological process and the outcome of this cross?

Options

A.
The pollen grains carrying the $S_2$ allele will fail to germinate or their pollen tubes will be arrested in the style.
B.
The style of the $S_1S_2$ pistil produces specific S-RNases that degrade the ribosomal RNA of the matching $S_2$ pollen tubes.
C.
The resulting progeny from this cross will have the genotypes $S_1S_3$ and $S_2S_3$ in an expected 1:1 ratio.
D.
The rejection of the $S_2$ pollen is determined by the diploid genotype ( $S_2S_3$ ) of the pollen-producing plant rather than the haploid pollen itself.

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Comparative_Analysis

Sharpen your ability to evaluate multiple scenarios and distinguish between competing potential answers.

Concepts Behind This Question

S-gene|Pollen_Tube_Growth|Nicotiana_alata

Why This Question Is Tricky

Common Mistakes

Conceptual Pivot: Students often confuse Gametophytic Self-Incompatibility (GSI) with Sporophytic Self-Incompatibility (SSI).

In GSI, the individual haploid pollen grain's allele dictates its survival.

If a student assumes the diploid parent's genotype dictates rejection (SSI), they would incorrectly assume the statement in Option D is true, failing to recognize that GSI relies on the haploid expression of the multiple allelic S-locus.

Quick Facts About This Question

Question Information

Subject	Biology
Chapter	Principles of Inheritance and Variation - Class 12
Concept	Multiple Allelism Limitation
Difficulty	8
Cognitive Load	5
Target Solve Time	120 sec
Access	Free