The gene A, B, D are present in one chromosome in the coupling phase of linkage. One of the double cross-over gametes has A-b-D gene combination. The gene which was in the middle of the sequence is:
Show Hint
- Double cross-over exchanges the middle gene.
- Flanking genes remain in parental combination.
- Identify the gene that changes in the double cross-over gamete.
- A
- B
- D
- Cannot determine
The Correct Option is B
Solution and Explanation
This question tests knowledge of gene mapping and double cross-overs.
Step 2: Detailed Explanation:
In a double cross-over, the middle gene is exchanged, while the flanking genes remain in their original combination.
The parental combination is: A-B-D (in coupling phase).
The double cross-over gamete is: A-b-D (b is different from the parental).
This indicates that gene B has been exchanged, while A and D remain in their original positions.
Thus, the gene in the middle is B.
Other options:
- A (A): Not the middle gene.
- D (C): Not the middle gene.
- Cannot determine (D): Can be determined.
Thus, B is the middle gene.
Step 3: Final Answer:
Thus, the gene in the middle is B, which corresponds to option (B).
[0.5cm]
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