Question

The following table summarizes the flowering time behavior (days to flower) and the transcript levels in four genotypes of a plant species.

Which one of the following genetic pathways best explains the observations shown in the table?
 

• A. A gene activates B, which suppresses flowering transition.
• B. A gene suppresses B, which promotes flowering transition.
• C. B gene activates A, which suppresses flowering transition.
• D. B gene suppresses A, which promotes flowering transition.

Hint:

In genetic pathways, the interaction between genes can be complex. In this case, the suppression of one gene by another (gene A suppressing gene B) results in a different flowering time phenotype.

Answer 1

The Correct Option is B

Let's analyze the data in the table:

- Wild type: The wild type has a normal flowering time of 30 days, with normal transcript levels for both gene A and gene B. This suggests that both genes are functioning properly in the wild type, and there is no interference between their activities.

- a mutant: In the a mutant, the days to flower are reduced to 15 days, with gene A showing no transcript levels (Nil) and gene B showing an increased transcript level. This suggests that when gene A is inactive, gene B is upregulated, leading to a faster flowering time. Hence, the activity of gene A seems to suppress gene B, and in its absence, gene B becomes more active, promoting flowering.

- b mutant: In the b mutant, the days to flower are delayed to 60 days, with normal transcript levels for gene A and no transcript for gene B. This suggests that gene B is crucial for the proper timing of flowering, and its absence leads to a delayed flowering time. The normal transcript level of gene A indicates that gene A alone does not prevent the flowering transition in the absence of gene B.

- ab double mutant: In the double mutant, the days to flower are still 60, with both genes showing Nil transcript levels. This suggests that both gene A and gene B are required for the normal regulation of flowering time, and their absence leads to a complete disruption of the flowering transition process.

Based on these observations, the pathway that best explains the data is that gene A suppresses gene B, and the absence of gene A leads to the upregulation of gene B, which accelerates the flowering transition. This supports option (B), which states that gene A suppresses gene B, which promotes flowering transition.

- (A): This option would suggest that gene A activates gene B and suppresses flowering, which is not supported by the data. Hence, statement (A) is incorrect.
- (C): This option would imply that gene B activates gene A and suppresses flowering, but the data shows that gene B's absence (in the b mutant) leads to delayed flowering, not accelerated. Hence, statement (C) is incorrect.
- (D): This option suggests that gene B suppresses gene A, but the data suggests that the lack of gene A leads to upregulation of gene B, not the other way around. Hence, statement (D) is incorrect.

Thus, the correct answer is (B).