From one F⁺strain,three distinct Hfr strains were derived.The first three markers transferred during an Hfr X F^- cross (different for each of the three Hfr) are:
Hfr 1: ...D A →
Hfr 2: ...E B →
Hfr 3: ...E C D →
Which of the following must be the order of the genes on the bacterial chromosomal circle? (A is shown at both ends to represent circularity.Assume that the Hfr picks up all intermediates between any two represented genes.)

Question

Quizplus · Accepted Answer

Based on the three transfer events, we can construct the following map:

A -- D -- C -- E -- B -- F -- A

Starting from A and following the order of genes transferred in each Hfr strain, we can see that this map is consistent with all three transfer events. Additionally, since the question states that the chromosome is circular, we know that the last marker transferred by each Hfr (F1F1F10) must be located adjacent to the first marker transferred (either A or F1F1F1S1). The only map that satisfies this requirement is the one in choice A.

From One F+ strain,three Distinct Hfr Strains Were Derived

From One F⁺strain,three Distinct Hfr Strains Were Derived