​22 transduction was used to map the fadL gene. The result of two-factor crosses between fadL and two linked markers, purF and aroC, are shown below.

​Which one of the following is the correct map for the three genes?​

Correct option is B

Explanation-

In P22 transduction, genes that are closer together are more likely to be co-transduced (i.e., transferred together).
                               → Higher co-transduction frequency = shorter distance
Given data:
Cross 1 (fadL purF⁺ selected):
                         fadL : 200
                         fadL⁺ : 800
=> Co-transduction frequency = 200 / (200+800) = 20%
Cross 2 (fadL aroC⁺ selected):
                          fadL : 400
                          fadL⁺ : 600
=> Co-transduction frequency = 400 / (400+600) = 40%
Cross 3 (aroC purF⁺ selected):
                          purF : 500
                          purF⁺ : 500
=> Co-transduction frequency = 500 / (500+500) = 50%
Interpretation:
From highest to lowest co-transduction frequency:
                                       aroC–purF = 50% → closest
                                       fadL–aroC = 40%
                                       fadL–purF = 20% → farthest
Conclusion: The correct gene order is - fadL — aroC — purF
This matches Option b
Correct answer: Option b